Vane pump

ABSTRACT

A vane pump includes: a rotor with slots; vanes mounted in the slots, and adapted to project from the slots; a cam ring surrounding the rotor; and a plate defining pump chambers in cooperation with the rotor, vanes and cam ring. The plate includes: a suction port; a discharge port; a first back pressure port that receives a suction-side fluid pressure, and hydraulically communicates with a first back pressure chamber corresponding to a first vane positioned in a suction region; and a second back pressure port that hydraulically communicates with a second back pressure chamber corresponding to a second vane whose distal end portion is positioned at a terminal end portion of the suction port. The second back pressure port includes: a first portion arranged to receive a discharge-side fluid pressure; and a throttling portion for restricting a fluid flow between the first portion and second back pressure chamber.

BACKGROUND OF THE INVENTION

The present invention relates to vane pumps.

Japanese Patent Application Publication No. 7-259754 discloses a variable displacement vane pump which includes: a rotor including a plurality of slots at its outside periphery; a plurality of vanes mounted in corresponding ones of the slots, and adapted to project from, and travel inwards and outwards of the corresponding slots; a cam ring adapted to be eccentric with respect to the rotor, the cam ring surrounding the rotor; and a plurality of pump chambers defined by the vanes, an inside peripheral surface of the cam ring, and an outside peripheral surface of the rotor, wherein the displacement of the pump changes with a change in the eccentricity of the cam ring with respect to the rotor. The vane pump is arranged so that when the distal end portion of a vane is positioned in a suction region or a discharge region, the proximal end portion of the vane is applied with a back pressure that is substantially identical to a pressure applied to the distal end portion, in order to reduce the resistance to the distal end portion of the vane when the vane slides on the inside peripheral surface of the cam ring, and thereby reduce a loss in power for driving the vane pump. The proximal end portion of the vane starts to be applied with a discharge-side fluid pressure (high pressure), when the vane is positioned in the suction region before entering the discharge region. This is intended for ensuring that even when the vane pump is operating at low temperature where the viscosity of working fluid is relatively high, the vane projects from the slot, so as to seal the pump chambers well, and thereby make the pump operate normally.

SUMMARY OF THE INVENTION

Such vane pumps as disclosed in Japanese Patent Application Publication No. 7-259754 can encounter a problem that noise is generated due to factors such as contact between components. Accordingly, it is desirable to provide a vane pump in which noise is suppressed.

According to one aspect of the present invention, a vane pump comprises: a rotor adapted to be rotated by a drive shaft, the rotor including a plurality of slots at an outside periphery of the rotor; a plurality of vanes mounted in corresponding ones of the slots, and adapted to project from, and travel inwards and outwards of the corresponding slots; a cam ring adapted to be eccentric with respect to the rotor, the cam ring surrounding the rotor; and a plate arranged to face an axial end of the rotor, and define a plurality of pump chambers in cooperation with the rotor, the vanes, and the cam ring, wherein the plate includes at a side facing the rotor: a suction port opened in a suction region in which each pump chamber gradually expands while moving along with rotation of the rotor; a discharge port opened in a discharge region in which each pump chamber gradually contracts while moving along with rotation of the rotor; a first back pressure port arranged to receive a suction-side fluid pressure, and hydraulically communicate with a proximal end portion of at least a first one of the slots corresponding to a first one of the vanes positioned in the suction region; and a second back pressure port arranged to hydraulically communicate with a proximal end portion of at least a second one of the slots corresponding to a second one of the vanes whose distal end portion is positioned at a terminal end portion of the suction port, wherein the second back pressure port includes: a first portion arranged to receive a discharge-side fluid pressure; and a throttling portion arranged to restrict a flow of fluid between the first portion and the proximal end portion of the second slot.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a continuously variable transmission (CVT) system to which a vane pump according to each embodiment of the present invention is adapted.

FIG. 2 is a partial sectional view of a vane pump according to a first embodiment of the present invention in an axial direction of a rotor under a condition that a side plate is removed.

FIG. 3 is a plan view of a first plate of the vane pump.

FIG. 4 is a sectional view of the first plate taken along the line IV-IV in FIG. 3.

FIG. 5 is a sectional view of the first plate taken along the line V-V in FIG. 3.

FIG. 6 is a sectional view of a portion of the vane pump, including a sectional view of the first plate taken along the line VI-VI in FIG. 3.

FIG. 7 is an enlarged view of a portion indicated by VII in FIG. 6, showing a sectional shape of a beginning end portion of a discharge-side back pressure port.

FIG. 8 is a sectional view of the vane pump taken along the line VIII-VIII in FIG. 6.

FIG. 9 is a graphic diagram showing a relationship among the cross-sectional flow area and circumferential length of the beginning end portion of the discharge-side back pressure port, and noise level.

FIG. 10 is a sectional view of a vane pump according to a first comparative example, which corresponds to the sectional view of FIG. 8.

FIG. 11 is a sectional view of a vane pump according to a second comparative example, which corresponds to the sectional view of FIG. 8.

FIGS. 12A to 12D are plan views of beginning end portions of discharge-side back pressure ports according to variations of a second embodiment of the present invention.

FIGS. 13A and 13B are side sectional views of beginning end portions of discharge-side back pressure ports according to variations of the second embodiment.

FIGS. 14A to 14D are plan views of beginning end portions of discharge-side back pressure ports according to variations of a third embodiment of the present invention.

FIG. 15 is a side sectional view of a beginning end portion of a discharge-side back pressure port according to a variation of the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment/Construction

The following describes construction of a vane pump (henceforth referred to as pump 1) according to a first embodiment of the present invention. Pump 1 is adapted to be used to supply hydraulic pressure to a hydraulic actuator in a motor vehicle. In this example, pump 1 is adapted to be used to supply hydraulic pressure to a belt-type continuously variable transmission (CVT 100). Pump 1 is not so limited, but may be used to supply hydraulic pressure to another hydraulic actuator such as a hydraulic actuator in a power steering system. Pump 1 is driven by a crankshaft of an internal combustion engine, to suck and discharge working fluid. In this example, working fluid is working oil such as ATF (automatic transmission fluid). A typical ATF has such a relatively small elastic modulus that a small change in volume of the ATF can cause a large change in pressure. FIG. 1 shows a system of CVT 100 to which pump 1 is adapted. CVT 100 includes a control valve unit 200 that is provided with various valves such as a shift control valve 201, a secondary valve 202, a secondary pressure solenoid valve 203, a line pressure solenoid valve 204, a pressure regulator valve 205, a manual valve 206, a lockup/select switch solenoid valve 207, a clutch regulator valve 208, a select control valve 209, a lockup solenoid valve 210, a torque converter regulator valve 211, a lockup control valve 212, and a select switch valve 213. These valves are controlled by a CVT control unit 300. Pump 1 discharges and supplies working fluid through control valve unit 200 to various parts of CVT 100 such as a primary pulley 101, a secondary pulley 102, a forward clutch 103, a reverse brake 104, a torque converter 105, and a lubricating and cooling system 106.

FIG. 2 is a partial sectional view of pump 1 in an axial direction of a rotor 6 under a condition that a side plate is removed. In the following description, a three dimensional normal coordinate system is assumed in which an x axis is defined to extend in a radial direction of pump 1, a y axis is defined to extend in another radial direction of pump 1, and a z axis is defined to extend in the axial direction of rotor 6. Specifically, the x axis is defined to extend in a direction where a central axis “P” of a cam ring 8 moves or swings with respect to an axis of rotation “O” of rotor 6. The y axis is defined to extend in a direction perpendicular to both of the x axis and z axis. FIG. 2 shows a view in the negative z-axis direction from the positive z side. In FIG. 2, the positive x-axis direction is a direction where the central axis P of cam ring 8 deviates from the axis of rotation O (or in a direction from a second closing region RE4 to a first closing region RE3 as detailed below and shown in FIG. 3). In FIG. 2, the positive y-axis direction is a direction from a suction region toward a discharge region.

Pump 1 is a variable displacement type capable of varying its displacement or discharge capacity or pump capacity, i.e. amount of fluid discharged per one rotation. Pump 1 includes a pumping section 2 for sucking and discharging working fluid, and a control section 3 for controlling the discharge capacity, which are integrated as a unit. Pumping section 2 is accommodated in a housing 4, including a drive shaft 5, a rotor 6, vanes 7, and a cam ring 8. Housing 4 includes a housing body 40, a first plate 41, and a second plate 42, which are fixed together, for example, by bolting.

Housing body 40 is formed with a substantially cylindrical through hole 400 which extends in the z-axis direction, and in which an annular adapter ring 9 is mounted. Adapter ring 9 includes a substantially cylindrical accommodation hole 90 that extends in the z-axis direction. Accommodation hole 90 is formed with a first flat portion 91 which is located on the positive x side, and substantially parallel to the y-z plane. Accommodation hole 90 is formed also with a second flat portion 92 which is located on the negative x side, and substantially parallel to the y-z plane. Second flat portion 92 is formed with a recess 920 which is located substantially at a central position of second flat portion 92 in the z-axis direction, and extends in the negative x-axis direction. Accommodation hole 90 is formed also with a third flat portion 93 which is located at the positive y side and slightly on the positive x side with respect to the axis of rotation O, and substantially parallel to the z-x plane. Third flat portion 93 is formed with a groove or recess 930 having a semicircular section as viewed in the z-axis direction. Third flat portion 93 is formed also with first and second communication passages 931 and 932 on both sides of recess 930. Specifically, first communication passage 931 opens in a portion of third flat portion 93 on the positive x side of recess 930, whereas second communication passage 932 opens in a portion of third flat portion 93 on the negative x side of recess 930. Accommodation hole 90 is formed also with a fourth flat portion 94 which is located at the negative y side, and substantially parallel to the z-x plane. Fourth flat portion 94 is formed with a groove or recess 940 having a rectangular section as viewed in the z-axis direction.

Cam ring 8 is mounted in accommodation hole 90 of adapter ring 9, and adapted to move or swing freely, wherein cam ring 8 has an annular shape. Adapter ring 9 is thus arranged to surround cam ring 8. As viewed in the z-axis direction, cam ring 8 has a substantially circular inside peripheral surface 80, and a substantially circular outside peripheral surface 81, where cam ring 8 has a substantially uniform radial thickness. The outside peripheral surface 81 of cam ring 8 is formed with a groove or recess 810 having a semicircular section as viewed in the z-axis direction, where recess 810 is located at the positive y side of outside peripheral surface 81. The outside peripheral surface 81 of cam ring 8 is formed also with a substantially cylindrical recess 811 having a central longitudinal axis extending in the x-axis direction, where recess 811 is located at the negative x side of outside peripheral surface 81. Between the recess 930 in the inside periphery of adapter ring 9 and the recess 810 in the outside periphery of cam ring 8 is mounted a pin 10 which extends in the z-axis direction, and is fitted in the space defined between recesses 930 and 810. In the recess 940 in the periphery of adapter ring 9 is mounted a seal 11. Seal 11 is in contact with the negative y side of outside peripheral surface 81 of cam ring 8. An elastic member such as a spring 12 is provided, which has a longitudinal end mounted in recess 920 in the inside periphery of adapter ring 9. Spring 12 is a coil spring. The other longitudinal end of spring 12 is mounted in recess 811 of cam ring 8. Spring 12 is mounted in a compressed state so as to constantly urge the cam ring 8 in the positive x-axis direction with respect to adapter ring 9 or housing 4. The size of accommodation hole 90 in the x-axis direction, i.e. the distance between the first flat portion 91 and second flat portion 92, is set larger than the diameter of outside peripheral surface 81 of cam ring 8. Cam ring 8 is supported by adapter ring 9 or housing 4 on third flat portion 93, for moving or swinging in the x-y plane about third flat portion 93 as a fulcrum. Pin 10 serves to restrict deviation or relative rotation of cam ring 8 with respect to adapter ring 9.

The swinging motion of cam ring 8 is restricted on the positive x side by contact between the outside peripheral surface 81 and the first flat portion 91 of adapter ring 9, and restricted on the negative x side by contact between the outside peripheral surface 81 and the second flat portion 92 of adapter ring 9. The eccentricity or distance of the central axis P of cam ring 8 with respect to the axis of rotation O is represented by O. When the outside peripheral surface 81 of cam ring 8 is in contact with the second flat portion 92 of adapter ring 9, the central axis P of cam ring 8 is located substantially at the axis of rotation O so that the eccentricity δ is equal to about zero. This position is called minimum eccentric position. On the other hand, when the outside peripheral surface 81 of cam ring 8 is in contact with the first flat portion 91 of adapter ring 9, the eccentricity δ is maximized. This position is called maximum eccentric position. While cam ring 8 is swinging, the third flat portion 93 of adapter ring 9 is in sliding contact with the outside peripheral surface 81 of cam ring 8, and the seal 11 in recess 940 is in sliding contact with outside peripheral surface 81. The positive z side and negative z side of the space between the inside periphery of adapter ring 9 and the outside periphery of cam ring 8 are sealed by first plate 41 and second plate 42, respectively, and divided fluid-tightly or liquid-tightly by third flat portion 93 and seal 11 into first and second control chambers R1 and R2. First control chamber R1 is located on the positive x side, whereas second control chamber R2 is located on the negative x side. First control chamber R1 hydraulically communicates with first communication passage 931, whereas second control chamber R2 hydraulically communicates with second communication passage 932. Under the conditions that the movement of cam ring 8 is restricted, a clearance is provided between the outside periphery of cam ring 8 and the inside periphery of adapter ring 9, so that the volumetric capacity of each of first and second control chambers R1 and R2 is constantly above zero.

Drive shaft 5 is rotatably supported by first and second plates 41 and 42 of housing 4. Drive shaft 5 is linked with the crankshaft of the internal combustion engine through a timing chain so that drive shaft 5 rotates in synchronization with the crankshaft. Rotor 6 is coaxially arranged with drive shaft 5, and coupled by spline coupling to the outside periphery of drive shaft 5. Rotor 6 has a substantially cylindrical shape, and is mounted inside the cam ring 8. Cam ring 8 is thus arranged to surround the rotor 6. In this way, an annular chamber R3 is defined between the inside peripheral surface 80 of cam ring 8 and an outside peripheral surface 60 of rotor 6, and between first and second plates 41 and 42. Rotor 6 rotates about the axis of rotation O in a clockwise direction as viewed in FIG. 2, along with drive shaft 5.

Rotor 6 is formed with a plurality of slots 61 which extend radially of rotor 6. Each slot 61 extends straight in a radial direction of rotor 6 from the outside peripheral surface 60 toward the axis of rotation O by a predetermined depth as viewed in the z-axis direction, and extends over the entire length of rotor 6 in the z-axis direction. Eleven slots 61 are arranged in the circumferential direction, and evenly spaced. Eleven vanes 7 are provided, each of which is a substantially rectangular plate, and is mounted in a corresponding one of slots 61, and adapted to project from, and travel inwards and outwards of slot 61. A distal end portion 70 of vane 7, which is outward in the radial direction of rotor 6, or one of end portions farther from the axis of rotation O, is curved to be fitted with the inside peripheral surface 80 of cam ring 8, as viewed in the z-axis direction. The number of slots 61 or vanes 7 is not limited to eleven. A proximal end portion 610 of slot 61, which is inward in the radial direction of rotor 6, or one of longitudinal end portions closer to the axis of rotation O, is formed in a substantially cylindrical shape as viewed in the z-axis direction, where the cylindrical shape has a diameter larger than the size of a main portion 611 of slot 61 in the circumferential direction of rotor 6. The shape of proximal end portion 610 is not limited to a cylindrical shape, but may be formed in a rectangular shape like the main portion 611. Between the proximal end portion 610 of slot 61 and a proximal end portion 71 of vane 7 which is inward in the radial direction of rotor 6, or one of the longitudinal end portions closer to the axis of rotation O, is defined a pressure-receiving portion or back pressure chamber “br”. The outside peripheral surface 60 of rotor 6 is formed with a plurality of projections 62 each of which is located at a corresponding one of vanes 7, and has a substantially trapezoidal section as viewed in the z-axis direction. Projection 62 extends over the entire length of rotor 6 in the z-axis direction, and extends from the outside peripheral surface 60 by a predetermined height in the radial direction of rotor 6. Slot 61 opens substantially at the center of projection 62 as viewed in the z-axis direction. The length of slot 61 in the radial direction of rotor 6, i.e. the total length including the proximal end portion 610 and projection 62, is set substantially equal to the length of vane 7 in the radial direction of rotor 6. The provision of projection 62 serves to constantly hold vane 7 in slot 61 even when vane 7 maximally projects from slot 61, for example, in the first closing region RE3. In other words, this structure serves to remove unnecessary portions from the outside peripheral surface 60 of rotor 6 except the projections 62, while ensuring that slot 61 constantly holds vane 7. This results in increase in the volumetric capacity of pump chambers “r”, increase in the pump efficiency, reduction in the weight of rotor 6, and reduction in the power loss.

The annular chamber R3 between rotor 6 and cam ring 8 is divided by eleven vanes 7 into eleven pump chambers r. In the following, the distance between two adjacent vanes 7 in the rotational direction of rotor 6 (the clockwise direction in FIG. 2, represented by RD1) is defined as a unit pitch. The length of pump chamber r in the rotor rotation direction RD1 is equal to one pitch and unchanged. When the central axis P of cam ring 8 is displaced or eccentric from the axis of rotation O in the positive x-axis direction, the distance between the outside peripheral surface 60 of rotor 6 and the inside peripheral surface 80 of cam ring 8 in the rotor radial direction (or the size of pump chamber r in the rotor radial direction) gradually increases as followed from the negative x side to the positive x side. Accordingly, the volumetric capacity of pump chamber r on the positive x side is larger than that of pump chamber r on the negative x side, where vane 7 travels inwards and outwards of slot 61 in accordance with a change in the size of pump chamber r in the rotor radial direction. As a result, in a region on the negative y side of the x axis, the volumetric capacity of pump chamber r gradually increases while moving along with rotation of rotor 6 in the rotor rotation direction RD1 (in the clockwise direction in FIG. 2) from the negative x side to the positive x side. On the other hand, in a region on the positive y side of the x axis, the volumetric capacity of pump chamber r gradually decreases while moving along with rotation of rotor 6 in the rotor rotation direction RD1 (in the clockwise direction in FIG. 2) from the positive x side to the negative x side.

First and second plates 41 and 42 are a pair of disc-shaped plates (pressure plates or side plates). First and second plates 41 and 42 are arranged to face both axial ends of rotor 6 (and vanes 7) and cam ring 8 in the z-axis direction, where rotor 6 (and vanes 7) and cam ring 8 are sandwiched therebetween. First plate 41 is arranged to face the negative z side of rotor 6 and others. FIG. 3 shows a plan view of first plate 41 from the positive z side. The outline of first plate 41 is schematically expressed with a circular shape, and bolt holes and the like are omitted. FIG. 4 is a sectional view of first plate 41 taken along the line IV-IV in FIG. 3. FIG. 5 is a sectional view of first plate 41 taken along the line V-V in FIG. 3. On the negative z side of first plate 41 is arranged a pump cover 49. FIG. 5 shows a sectional view of pump cover 49. Pump cover 49 is formed with a through hole 490, a first communication passage 491, and a second communication passage 492. Drive shaft 5 is inserted and rotatably supported in through hole 490. First communication passage 491 is in the form of a groove for suction-side communication which is formed in a positive z side surface of pump cover 49, and positioned to overlap with negative z side openings of a communication hole 451 and a communication hole 432 of first plate 41 which are described in detail below. The positive z side surface of pump cover 49 is formed also with a seal groove 494 which surrounds the second communication passage 492. An O-ring 496 is mounted in seal groove 494 for sealing. Under a condition that the negative z side surface of first plate 41 is placed to face the positive z side surface of pump cover 49, the O-ring 496 is compressed in the z-axis direction into tight contact with the negative z side surface of first plate 41, to improve the liquid tightness of second communication passage 492 that is subject to high pressure.

First plate 41 is formed with a suction port 43, a discharge port 44, a suction-side back pressure port 45, a discharge-side back pressure port 46, a pin hole 47, and a through hole 48. Pin 10 is inserted and fixed in pin hole 47. Drive shaft 5 is inserted and rotatably supported in through hole 48. Second plate 42 is formed with similar ports and holes in similar positions. However, the ports of second plate 42 may be omitted. In the first embodiment, the construction that both of first and second plates 41 and 42 are formed with such similar ports, is effective for bringing into balance hydraulic forces which are applied from discharge port 44 and the like to rotor 6 and vanes 7 in the z-axis direction, and thereby suppressing the tear and resistance resulting from unbalanced contact. Alternatively, suction port 43 and the like may be distributed to first and second plates 41 and 42 as appropriate.

Suction port 43 is arranged in a suction region or section RE1 on the negative y side of first plate 41 where pump chamber r gradually expands while moving along with rotation of rotor 6. Working fluid is supplied through suction port 43 from the outside to pump chambers r located in the suction region RE1. Suction port 43 includes a suction-side arc groove 430, a suction hole 431, and a communication hole 432. Suction-side arc groove 430 is formed in a positive z side surface 410 of first plate 41, and arranged to receive a suction-side fluid pressure. As viewed in the z-axis direction, the suction-side arc groove 430 has the form of an arc about the axis of rotation O, extending in a circumferential direction of first plate 41 through a portion in which pump chambers r are arranged in suction region RE1. The suction region RE1 of pump 1 is defined by an angular range of suction-side arc groove 430, i.e. by an angle α defined by a straight line connecting the axis of rotation O to a beginning end point “A” of suction-side arc groove 430 on the negative x side of first plate 41 and a straight line connecting the axis of rotation O to a terminal end point “B” of suction-side arc groove 430 on the positive x side of first plate 41. The angle α is equivalent to about 4.5 pitches in this example. Each of the beginning end point A and terminal end point B of suction-side arc groove 430 is positioned away from the x axis by an angle f3 in the negative y-axis direction, where the angle β is equivalent to about 0.5 pitch in this example.

Suction-side arc groove 430 is provided with a semicircular terminal end portion 436 that projects in the rotor rotation direction RD1. Suction-side arc groove 430 is provided with a beginning end portion 435 that includes a main section beginning end portion 433 having a semicircular shape projecting in a direction opposite to the rotor rotation direction RD1 (referred to as rotor reverse rotation direction), and a notch 434 formed continuous with main section beginning end portion 433. Notch 434 extends in the rotor reverse rotation direction from main section beginning end portion 433 by about 0.5 pitch to the beginning end point A. The width of suction-side arc groove 430 in the rotor radial direction is substantially uniform over the entire length in the circumferential direction, and substantially equal to the width of annular chamber R3 in the rotor radial direction when cam ring 8 is in the minimum eccentric position, as shown in FIG. 2. Suction-side arc groove 430 has an inside radial edge 437 which is positioned somewhat outside of the outside peripheral surface 60 (except projections 62) of rotor 6 in the rotor radial direction. Suction-side arc groove 430 has an outside radial edge 438 which is positioned somewhat outside of the inside peripheral surface 80 of cam ring 8 in the rotor radial direction when cam ring 8 is in the minimum eccentric position, and positioned slightly outside of the inside peripheral surface 80 of cam ring 8 in the rotor radial direction when cam ring 8 is in the maximum eccentric position. Wherever cam ring 8 is positioned, pump chambers r in the suction region overlap with suction-side arc groove 430 as viewed in the z-axis direction and hydraulically communicate with suction-side arc groove 430. Suction hole 431 is opened substantially at the center of suction-side arc groove 430 in the circumferential direction. Suction hole 431 has a substantially elliptic shape as viewed in the z-axis direction, and has a width in the rotor radial direction which is substantially equal to the width of suction-side arc groove 430, and a length in the circumferential direction which is equal to about one pitch. Suction hole 431 is located to overlap with the y axis as viewed in the z-axis direction, extending through first plate 41 in the z-axis direction. Communication hole 432 is opened in suction-side arc groove 430, and arranged adjacent to suction hole 431 and in the rotor reverse rotation direction from suction hole 431 (closer to the beginning end point A than suction hole 431). Communication hole 432 has a similar shape as suction hole 431, extending through first plate 41 in the z-axis direction. In suction-side arc groove 430, the depth of the main section beginning end portion 433, the portion between communication hole 432 and suction hole 431, and the terminal end portion 436 in the z-axis direction is smaller than or equal to 20% of the thickness of first plate 41 in the z-axis direction. The portion between main section beginning end portion 433 and communication hole 432 is inclined so that the depth gradually increases as followed in the rotor rotation direction RD1, and becomes equal to the thickness of first plate 41 at communication hole 432. The portion between suction hole 431 and terminal end portion 436 is inclined so that the depth gradually decreases as followed in the rotor rotation direction RD1, becomes equal to the depth of main section beginning end portion 433 at terminal end portion 436. The notch 434 is in the form of an acute angle triangle whose width in the rotor radial direction gradually increases as followed in the rotor rotation direction RD1, as viewed in the z-axis direction. The maximum width of notch 434 in the rotor radial direction is set smaller than that of suction-side arc groove 430. The depth of notch 434 in the z-axis direction is set to increase from zero to several % of the thickness of first plate 41 as followed in the rotor rotation direction RD1. Accordingly, the cross-sectional flow area of notch 434 is set smaller than the main section of suction-side arc groove 430, and set to gradually increase as followed in the rotor rotation direction RD1, thus forming a throttling portion. Discharge port 44 is arranged in a discharge region or section RE2 on the positive y side of first plate 41 where pump chamber r gradually contracts while moving along with rotation of rotor 6. Working fluid is discharged through discharge port 44 to the outside from pump chambers r located in the discharge region RE2. Discharge port 44 includes a discharge-side arc groove 440, a communication hole 441, and a discharge hole 442. Discharge-side arc groove 440 is formed in the positive z side surface 410 of first plate 41, and arranged to receive a discharge-side fluid pressure. As viewed in the z-axis direction, the discharge-side arc groove 440 has the form of an arc about the axis of rotation O, extending in the circumferential direction of first plate 41 through a portion in which pump chambers r are arranged in the discharge region RE2. The discharge region RE2 of pump 1 is defined by an angular range of discharge-side arc groove 440, i.e. by an angle α defined by a straight line connecting the axis of rotation O to a beginning end point “C” of discharge-side arc groove 440 on the positive x side of first plate 41 and a straight line connecting the axis of rotation O to a terminal end point “D” of discharge-side arc groove 440 on the negative x side of first plate 41. The angle α is equivalent to about 4.5 pitches in this example. Each of the beginning end point C and terminal end point D of discharge-side arc groove 440 is positioned away from the x axis by an angle β in the positive y-axis direction, where the angle β is equivalent to about 0.5 pitch in this example. Discharge-side arc groove 440 is provided with a rectangular beginning end portion 443. The width of discharge-side arc groove 440 in the rotor radial direction is substantially uniform over the entire length in the circumferential direction, and slightly smaller than that of suction-side arc groove 430. Discharge-side arc groove 440 has an inside radial edge 446 which is positioned somewhat outside of the outside peripheral surface 60 (except projections 62) of rotor 6 in the rotor radial direction. Discharge-side arc groove 440 has an outside radial edge 447 which is positioned substantially identical to the inside peripheral surface 80 of cam ring 8 in the rotor radial direction when cam ring 8 is in the minimum eccentric position. Wherever cam ring 8 is positioned, pump chambers r in the discharge region RE2 overlap with discharge-side arc groove 440 as viewed in the z-axis direction and hydraulically communicate with discharge-side arc groove 440. Discharge hole 442 is opened in a terminal end portion 444 of discharge-side arc groove 440 which is located on the side of rotor rotation direction RD1 of discharge-side arc groove 440. Discharge hole 442 has a substantially elliptic shape as viewed in the z-axis direction, and has a width in the rotor radial direction which is substantially equal to the width of discharge-side arc groove 440, and a length in the circumferential direction which is somewhat larger than one pitch. Discharge hole 442 is formed to extend through first plate 41 in the z-axis direction. Discharge hole 442 has a semicircular edge that projects in the rotor rotation direction RD1, and substantially identical to the semicircular edge of terminal end portion 444 as viewed in the z-axis direction. Communication hole 441 is opened on the side of rotor reverse rotation direction of discharge-side arc groove 440, which is located in a position opposite to the position of communication hole 432 with respect to the axis of rotation O as viewed in the z-axis direction. Communication hole 441 has a similar shape as discharge hole 442 and a length of about one pitch in the circumferential direction, extending through first plate 41 in the z-axis direction. The beginning end portion 443 of discharge-side arc groove 440 extends from the beginning end point C to a rotor reverse rotation direction side edge 445 of communication hole 441. The rotor reverse rotation direction side edge 445 is in the form of a semicircle projecting in the rotor reverse rotation direction as viewed in the z-axis direction, and has a leading end point “E” which is located about one pitch from the beginning end point C in the rotor rotation direction RD1. The leading edge of beginning end portion 443 facing the terminal end point B of suction-side arc groove 430 in the rotor reverse rotation direction is formed straight, extending in the rotor radial direction, as viewed in the z-axis direction. In discharge-side arc groove 440, the depth (in the z-axis direction) of a main section 448 between communication hole 441 and discharge hole 442 is equal to about 25% of the thickness of first plate 41 in the z-axis direction. The depth of beginning end portion 443 in the z-axis direction is smaller than that of main section 448, and changes as followed from the beginning end point C to the rotor reverse rotation direction side edge 445 of communication hole 441. Specifically, the depth of beginning end portion 443 at the beginning end point C is equal to zero, and set to gradually increase as followed toward the rotor reverse rotation direction side edge 445, and become smaller than or equal to about 10% of the thickness of first plate 41 at the rotor reverse rotation direction side edge 445. The cross-sectional flow area of beginning end portion 443 is set smaller than that of main section 448, and set to gradually increase as followed in the rotor rotation direction RD1, thus forming a throttling portion.

In the positive z side surface 410 of first plate 41, no groove is formed between the terminal end point B of suction-side arc groove 430 and the beginning end point C of discharge-side arc groove 440. This region is called first closing region RE3 which is defined by an angle of 2β made by a straight line connecting the axis of rotation O to the terminal end point B of suction-side arc groove 430 and a straight line connecting the axis of rotation O to the beginning end point C of discharge-side arc groove 440. The angle 2β is equivalent to about one pitch. Similarly, in the positive z side surface 410 of first plate 41, no groove is formed between the terminal end point D of discharge-side arc groove 440 and the beginning end point A of suction-side arc groove 430. This region is called second closing region RE4 which is defined by an angle of 2β made by a straight line connecting the axis of rotation O to the terminal end point D of discharge-side arc groove 440 and a straight line connecting the axis of rotation O to the beginning end point A of suction-side arc groove 430. The angle 2β is equivalent to about one pitch. When pump chamber r is positioned in the first closing region RE3 or second closing region RE4, the working fluid in pump chamber r is closed so as to prevent fluid communication between suction-side arc groove 430 and discharge-side arc groove 440. Each of the first closing region RE3 and second closing region RE4 extends across the x axis.

First plate 41 is formed with a suction-side back pressure port 45 and a discharge-side back pressure port 46 which are provided independently of each other, and arranged to hydraulically communicate with the root of each vane 7 (back pressure chamber br formed in the proximal end portion 610 of slot 61). Suction-side back pressure port 45 is arranged to hydraulically connect the suction port 43 to back pressure chambers br corresponding to most of vanes 7 located in the suction region RE1, specifically, back pressure chambers br corresponding to vanes 7 whose distal end portions 70 overlap with suction port 43 (suction-side arc groove 430). Suction-side back pressure port 45 includes a suction-side back pressure arc groove 450, and a communication hole 451. Suction-side back pressure arc groove 450 is formed in the positive z side surface 410 of first plate 41, and arranged to receive a suction-side fluid pressure. As viewed in the z-axis direction, suction-side back pressure arc groove 450 has the form of an arc about the axis of rotation O, extending in the circumferential direction of first plate 41 through a portion in which back pressure chambers br (proximal end portion 610 of rotor 6) for vanes 7 are arranged. Suction-side back pressure arc groove 450 extends over an angular range of about three pitches, which is smaller than that of suction-side arc groove 430. Suction-side back pressure arc groove 450 has a beginning end point “a” that is located slightly ahead of the beginning end point A of notch 434 or suction-side arc groove 430, and adjacent to main section beginning end portion 433, in the rotor rotation direction RD1. Suction-side back pressure arc groove 450 has a terminal end point “b” that is located about 1.5 pitches behind the terminal end point B of suction-side arc groove 430 in the rotor rotation direction RD1. The size of suction-side back pressure arc groove 450 in the rotor radial direction is substantially uniform over the entire length in the circumferential direction, and substantially equal to that of suction-side arc groove 430, and substantially equal to that of proximal end portion 610 of slot 61. Suction-side back pressure arc groove 450 has an inside radial edge 454 that is located somewhat inside the inside radial edge of proximal end portion 610 of slot 61 in the rotor radial direction. Suction-side back pressure arc groove 450 has an outside radial edge 455 that is located slightly inside the outside radial edge of proximal end portion 610 of slot 61 in the rotor radial direction. Wherever cam ring 8 is positioned, suction-side back pressure arc groove 450 overlaps with most of back pressure chambers br (proximal end portions 610 of slots 61) as viewed in the z-axis direction so as to hydraulically communicate with the same. Communication hole 451 is located on the rotor reverse rotation direction side of suction-side back pressure port 45, closer to the beginning end point a than to the terminal end point b, and overlaps with communication hole 432 of suction-side arc groove 430 in the circumferential direction. Communication hole 451 has a substantially elliptic shape as viewed in the z-axis direction, and has a width in the rotor radial direction which is substantially equal to the width of suction-side back pressure arc groove 450, and a length in the circumferential direction which is equal to about one pitch. Communication hole 451 extends through first plate 41 in the z-axis direction, and hydraulically communicates with communication hole 432 of suction-side arc groove 430 through first communication passage 491. In suction-side back pressure arc groove 450, a beginning end portion 452 is formed between the beginning end point a and suction hole 431. As viewed in the z-axis direction, beginning end portion 452 has a semicircular end which projects in the rotor reverse rotation direction. Suction-side back pressure arc groove 450 has a semicircular terminal end portion 453 which projects in the rotor rotation direction RD1. The depth of beginning end portion 452 in the z-axis direction is equal to about 40% or smaller of the thickness of first plate 41, whereas the depth of terminal end portion 453 in the z-axis direction is equal to about 20% or smaller of the thickness of first plate 41. The portion between terminal end portion 453 and communication hole 451 is inclined so that the depth gradually increases as followed toward communication hole 451, and becomes equal to the thickness of first plate 41 at communication hole 451.

Discharge-side back pressure port 46 is arranged to hydraulically connect the discharge port 44 to back pressure chambers br corresponding to vanes 7 which are located in the discharge region RE2, the first closing region RE3, a major part of the second closing region RE4, and a part of the suction region RE1, specifically, back pressure chambers br corresponding to vanes 7 whose distal end portion 70 overlaps with discharge port 44, the part of suction-side back pressure port 45, the first closing region RE3, or the major part of the second closing region RE4. Discharge-side back pressure port 46 includes a discharge-side back pressure arc groove 460, and a communication hole 461. Discharge-side back pressure arc groove 460 is formed in the positive z side surface 410 of first plate 41, and arranged to receive a discharge-side fluid pressure. As viewed in the z-axis direction, discharge-side back pressure arc groove 460 has the form of an arc about the axis of rotation O, extending in the circumferential direction of first plate 41 through a portion in which back pressure chambers br (proximal end portion 610 of rotor 6) for vanes 7 are arranged. Discharge-side back pressure arc groove 460 extends over an angular range of about seven pitches, which is larger than that of discharge-side arc groove 440. Discharge-side back pressure arc groove 460 extends through the first closing region RE3, and extends in the suction region RE1, having a beginning end point “c” that is located behind the beginning end point C of discharge-side arc groove 440, and further behind the terminal end point B of suction-side arc groove 430, in the rotor rotation direction RD1. The beginning end point c of discharge-side back pressure arc groove 460 is located about one pitch (equivalent to the angle of 2β behind the terminal end point B of suction-side arc groove 430 in the rotor rotation direction RD1. A terminal end point “d” of discharge-side back pressure arc groove 460 is located about one pitch or smaller ahead of the terminal end point D of discharge-side arc groove 440, and thus located closer to the terminal end point of the second closing region RE4, in the rotor rotation direction RD1. The size of discharge-side back pressure arc groove 460 in the rotor radial direction is substantially uniform over the entire length in the circumferential direction, and slightly smaller than that of discharge-side arc groove 440, and somewhat smaller than that of proximal end portion 610 of slot 61. Discharge-side back pressure arc groove 460 has an inside radial edge 464 that is located somewhat outside of the inside edge of proximal end portion 610 in the rotor radial direction. Discharge-side back pressure arc groove 460 has an outside radial edge 465 that is located slightly inside the outside edge of proximal end portion 610 in the rotor radial direction. Wherever cam ring 8 is positioned, discharge-side back pressure arc groove 460 overlaps with most of back pressure chambers br (proximal end portions 610 of slots 61) as viewed in the z-axis direction so as to hydraulically communicate with the same. Communication hole 461 is located closer to the beginning end point c than to the terminal end point d, and in an angular position between the terminal end point B of suction-side arc groove 430 and the x axis (midpoint in the first closing region RE3) on the beginning end side of the first closing region RE3. The diameter of communication hole 461 is substantially equal to the width of discharge-side back pressure arc groove 460 in the rotor radial direction. Communication hole 461 is formed to extend through first plate 41 with such an inclination relative to the z axis that the cross-section of communication hole 461 as viewed in the z-axis direction moves outwards in the rotor radial direction as followed in the negative z-axis direction. Communication hole 461 is opened in the negative z side surface of first plate 41, and arranged to hydraulically communicate with communication hole 441 of discharge port 44 (discharge-side arc groove 440) through second communication passage 492.

Discharge-side back pressure arc groove 460 includes a beginning end portion 462, and a back pressure port main section 468. FIG. 6 is a sectional view of pumping section 2 of pump 1, including a sectional view of first plate 41 taken along the line VI-VI in FIG. 3. Back pressure port main section 468 is a main section of discharge-side back pressure arc groove 460, extending from a beginning end point “e” to the terminal end point d. The beginning end point e is located about 0.4 pitch or smaller behind the terminal end point B of suction port 43 in the rotor rotation direction RD1. The depth of back pressure port main section 468 in the z-axis direction is substantially uniform. As viewed in the z-axis direction, the beginning end edge 467 of back pressure port main section 468 is substantially in the form of a semicircle projecting in the rotor reverse rotation direction. The terminal end edge 463 of back pressure port main section 468 or discharge-side back pressure arc groove 460 is substantially in the form of a semicircle projecting in the rotor rotation direction RD1. Beginning end portion 462, which is located on the rotor reverse rotation direction side of discharge-side back pressure arc groove 460 or behind back pressure port main section 468 in the rotor rotation direction RD1, extending in the suction region RE1 from the beginning end point c toward the edge 467 (beginning end point e) by 0.5 pitch or more in the rotor rotation direction RD1. The leading end of beginning end portion 462 facing the terminal end point b of suction-side back pressure arc groove 450 is substantially rectangular with a straight edge extending in the rotor radial direction. FIG. 7 is an enlarged view of a portion of pumping section 2 indicated by VII in FIG. 6, showing a sectional shape of beginning end portion 462. The bottom (negative z side surface) of beginning end portion 462 is substantially flat. As viewed in the rotor rotation direction RD1, beginning end portion 462 has a rectangular section that is substantially constant as followed in the rotor rotation direction RD1. The depth (length in the z-axis direction) of beginning end portion 462 is substantially uniform. Beginning end portion 462 serves as a throttling portion which has a smaller cross-sectional flow area than back pressure port main section 468. In the first embodiment, the cross section of beginning end portion 462 as viewed in the rotor rotation direction RD1 is not limited to rectangular shapes, but may have any shape if the cross-sectional flow area is substantially uniform as followed in the rotor rotation direction RD1. For example, beginning end portion 462 may have a cross-section with a moderately projected portion at the center of the bottom. The ratio of the depth of beginning end portion 462 with respect to that of back pressure port main section 468 may be selected arbitrarily. Second plate 42 includes a discharge-side back pressure arc groove 460, similar to first plate 41. The discharge-side back pressure arc groove 460 of second plate 42 includes a back pressure port main section 468 that extends from the beginning end point e, similar to the back pressure port main section 468 of first plate 41, but includes no beginning end portion 462 in contrast to first plate 41. Namely, a portion of the negative z side surface of second plate 42 that faces the beginning end portion 462 of first plate 41 is formed with no recess. This feature serves to enhance a throttling function of the beginning end portion 462 of first plate 41 which is described in detail below. However, second plate 42 may be provided with beginning end portion 462 in discharge-side back pressure arc groove 460, similar to first plate 41.

As shown in FIG. 6, the clearance between rotor 6 and first or second plate 41 or 42 in the z-axis direction is set small enough to prevent flow of working fluid in places (first closing region RE3, etc.) where discharge-side back pressure arc groove 460 does not extend. On the other hand, in the place where discharge-side back pressure arc groove 460 is provided, working fluid flows through discharge-side back pressure arc groove 460 between rotor 6 and first or second plate 41 or 42. Communication hole 461 is provided with an orifice 466 in a passage leading to discharge-side back pressure port 46 (discharge-side back pressure arc groove 460). Orifice 466 serves to restrict the flow passage of working fluid from discharge-side back pressure port 46 to discharge port 44, and thereby maintain the internal pressure of discharge-side back pressure port 46 to be high, promote the projection of vane 7, and enhance the startability of pump 1.

Referring back to FIG. 2, control section 3 is mounted in housing 4, including a control valve 30, first and second fluid passages 31 and 32, and first and second control chambers R1 and R2. Control valve 30 is a hydraulically-controlled valve, such as a spool valve, which includes a spool 302 mounted in an accommodation hole 401 formed in housing body 40, and a solenoid 301 mounted in housing 4 for actuating the spool 302, so as to switch the supply of working fluid between first fluid passage 31 and second fluid passage 32 formed in housing body 40. First fluid passage 31 and first communication passage 931 constitute a first control fluid passage. Second fluid passage 32 and second communication passage 932 constitute a second control fluid passage. Operation of control valve 30 is controlled by CVT control unit 300, on the basis of parameters, such as engine speed and throttle valve opening.

<Pumping Function> When rotor 6 is rotated under a condition that cam ring 8 is positioned eccentric in the positive x-axis direction with respect to the axis of rotation O, each pump chamber r expands and contracts periodically while revolving about the axis of rotation O. Working fluid is sucked through suction port 43 to each pump chamber r in the suction region RE1 on the negative y side where pump chamber r expands while moving along with rotation of rotor 6, and working fluid is discharged through discharge port 44 from each pump chamber r in the discharge region RE2 on the negative y side where pump chamber r contracts while moving along with rotation of rotor 6. Specifically, in the suction region RE1, each pump chamber r continues to expand until the rotor reverse rotation direction side vane 7 (rear-side vane 7) of pump chamber r passes through the terminal end point B of suction-side arc groove 430, namely, until the rotor rotation direction side vane 7 (front-side vane 7) of pump chamber r passes through the beginning end point C of discharge-side arc groove 440. During this period, pump chamber r is maintained hydraulically connected to suction-side arc groove 430, sucking working fluid through suction port 43. When each pump chamber r is positioned in the first closing region RE3, i.e. when the rotor rotation direction side surface of the rear-side vane 7 of pump chamber r is positioned at the terminal end point B of suction-side arc groove 430, and the rotor reverse rotation direction side surface of the front-side vane 7 of pump chamber r is positioned at the beginning end point C of discharge-side arc groove 440, pump chamber r is hydraulically separated from both of suction-side arc groove 430 and discharge-side arc groove 440, and thereby liquid-tightly closed. After the rotor rotation direction side surface of the rear-side vane 7 of pump chamber r passes through the terminal end point B of suction-side arc groove 430, and the rotor reverse rotation direction side surface of the front-side vane 7 of pump chamber r passes through the beginning end point C of discharge-side arc groove 440, pump chamber r contracts while moving along with rotation of rotor 6, and gets hydraulically connected to discharge-side arc groove 440, so as to discharge working fluid through discharge port 44. Similarly, when each pump chamber r is positioned in the second closing region RE4, i.e. when the rotor rotation direction side surface of the rear-side vane 7 of pump chamber r is positioned at the terminal end point D of discharge-side arc groove 440, and the rotor reverse rotation direction side surface of the front-side vane 7 of pump chamber r is positioned at the beginning end point A of suction-side arc groove 430, pump chamber r is hydraulically separated from both of suction-side arc groove 430 and discharge-side arc groove 440, and thereby liquid-tightly closed. In the first embodiment, each of the first closing region RE3 and second closing region RE4 has a range of one pitch (i.e. the width of pump chamber r in the circumferential direction). This serves to prevent fluid communication between the suction region RE1 and discharge region RE2, while enhancing the pump efficiency. However, each of the first closing region RE3 and second closing region RE4 (the spacing between suction port 43 and discharge port 44) is not limited to one pitch, but may have an angular range of more than one pitch. Namely, the range of each of the first closing region RE3 and second closing region RE4 may be arbitrarily set if fluid communication can be prevented between the suction region RE1 and the discharge region RE2. When the rotor reverse rotation direction side surface of the front-side vane 7 of pump chamber r moves from the first closing region RE3 to the discharge region RE2, the throttling function of the beginning end portion 443 of discharge-side arc groove 440 serves to prevent rapid fluid communication between pump chamber r and discharge-side arc groove 440, and thereby suppress fluctuations in the internal pressures of discharge port 44 and pump chamber r. This prevents working fluid from rapidly flowing through discharge port 44 having a higher pressure to pump chamber r having a lower pressure, and thereby prevents rapid decrease in the flow rate of working fluid supplied to the outside pipe that is connected to discharge port 44 through discharge hole 442. This suppresses fluid striking in the pipe, namely, fluctuations in fluid pressure in the pipe. Since the flow rate of working fluid supplied to pump chamber r is thus prevented from rapidly increasing, the internal pressure of pump chamber r is prevented from fluctuating. However, beginning end portion 443 of discharge-side arc groove 440 may be omitted or modified arbitrarily. On the other hand, when the rotor reverse rotation direction side surface of the front-side vane 7 of pump chamber r moves from the second closing region RE4 to the suction region RE1, the throttling function of the notch 434 of suction port 43 serves to prevent rapid fluid communication between pump chamber r and suction-side arc groove 430, and thereby suppress fluctuations in the internal pressures of suction port 43 and pump chamber r. This prevents working fluid from rapidly flowing from pump chamber r having a higher pressure to suction port 43 having a lower pressure, and thereby prevents occurrence of bubbles (cavitation). However, the notch 434 may be omitted or modified arbitrarily.

<Variable Displacement> When cam ring 8 is positioned eccentric in the positive x-axis direction with respect to the axis of rotation O so that the eccentricity δ is above zero, pump chamber r expands while moving along with rotation of rotor 6 on the negative y side. The volumetric capacity of pump chamber r is maximized when pump chamber r is positioned on the positive x side of the x axis in the first closing region RE3. On the other hand, pump chamber r contracts while moving along with rotation of rotor 6 on the positive y side. The volumetric capacity of pump chamber r is minimized when pump chamber r is positioned on the negative x side of the x axis in the second closing region RE4. When cam ring 8 is positioned in the maximum eccentric position as shown in FIG. 2, the difference in volumetric capacity between the minimally contracted pump chamber r and the maximally expanded pump chamber r is maximized, so that the pump capacity is maximized. On the other hand, when cam ring 8 is moved in the negative x-axis direction into the minimum eccentric position so that the eccentricity δ becomes zero, pump chamber r does not expand nor contract while moving along with rotation of rotor 6 anywhere on the positive y side and the negative y side. The difference in volumetric capacity between the minimally contracted pump chamber r and the maximally expanded pump chamber r is thus minimized to zero, so that the pump capacity is minimized to zero. In this way, as the eccentricity of cam ring 8 changes, the difference in volumetric capacity changes, so that the pump capacity changes.

When no working fluid is supplied to first control chamber R1 and second control chamber R2, cam ring 8 is positioned eccentric in the positive x-axis direction under the biasing force of spring 12, so that the eccentricity b is maximized. First control chamber R1 is supplied with working fluid from control valve 30 through the first control fluid passage. The supplied fluid pressure serves to produce a first hydraulic force for pressing the cam ring 8 in the negative x-axis direction against the biasing force of spring 12. On the other hand, second control chamber R2 is supplied with working fluid from control valve 30 through the second control fluid passage. The supplied fluid pressure serves to produce a second hydraulic force for pressing the cam ring 8 in the positive x-axis direction in addition to the biasing force of spring 12. CVT control unit 300 controls operation of control valve 30, and thereby changes the first and second hydraulic forces by suitable supply and drain of working fluid to and from first and second control chambers R1 and R2. This operation causes movement of cam ring 8, so that the eccentricity b changes. In this way, CVT control unit 300 controls the pump capacity. More specifically, when the hydraulic pressure in first control chamber R1 is increased, the first hydraulic force is increased. On the other hand, when the hydraulic pressure in second control chamber R2 is increased, the second hydraulic force is increased. When the resultant force of the first and second hydraulic forces is in the negative x-axis direction and the resultant force is larger than the biasing force of spring 12 for pressing the cam ring 8 in the positive x-axis direction, then cam ring 8 moves in the negative x-axis direction. This results in reduction in the eccentricity δ, and reduction in the difference in volumetric capacity between the contacted state and the expanded state, and thereby results in increase in the pump capacity. Second control chamber R2 may be omitted so that only first control chamber R1 serves to move cam ring 8. The device for constantly biasing the cam ring 8 is not limited to coil springs, but may be implemented differently. When the internal combustion engine is operating in a predetermined high speed region, the capacity of pump 1 is controlled to be small but sufficient, in order to reduce the torque required to drive the pump 1. This feature is advantageous, as compared to fixed displacement pumps.

<Reduction in Power Loss by Provision of Different Kinds of Back Pressure Ports> When rotor 6 is rotating, vane 7 is subject to a centrifugal force acting outwards in the rotator radial direction. Accordingly, when a predetermined condition is satisfied which includes a requirement that the rotational speed of rotor 6 is sufficiently high, the distal end portion 70 of vane 7 projects form slot 61 so as to contact the inside peripheral surface 80 of cam ring 8. The contact restricts outward movement of vane 7 in the rotor radial direction. When vane 7 moves outwards of slot 61, the back pressure chamber br behind the vane 7 expands. On the other hand, when vane 7 moves inwards of slot 61, the back pressure chamber br behind the vane 7 contracts. When rotor 6 is rotating under a condition that cam ring 8 is positioned eccentric in the positive x-axis direction from the axis of rotation O, the back pressure chamber br for each vane 7 in contact with the inside peripheral surface 80 of cam ring 8 expands and contracts periodically along with rotation of rotor 6. On the negative y side where back pressure chamber br is expanding, it is possible that the distal end portion 70 of vane 7 fails to be in contact with the inside peripheral surface 80 of cam ring 8, and thereby establish the liquid-tightness of pump chamber r, if a sufficient amount of working fluid is not supplied so as to allow projection of vane 7. On the other hand, on the positive y side where back pressure chamber br is contracting, it is possible that the distal end portion 70 of vane 7 undergoes a high frictional resistance in contact with the inside peripheral surface 80 of cam ring 8, if working fluid is not smoothly discharged from back pressure chamber br so as to allow inward movement or retraction of vane 7 into slot 61. In pump 1, on the negative y side, back pressure chamber br is supplied with working fluid from suction-side back pressure port 45. This serves to improve the outward movement of vane 7.

On the positive y side, working fluid is discharged from back pressure chamber br to discharge-side back pressure port 46. This serves to reduce the resistance against the sliding movement of vane 7. On the negative y side, the distal end portion 70 of vane 7 is subject to pressure from suction port 43, whereas the proximal end portion 71 of vane 7 is subject to pressure from suction-side back pressure port 45. Since suction-side back pressure port 45 is hydraulically connected to suction port 43 through first communication passage 491, the internal pressure of suction port 43 is substantially equal to that of suction-side back pressure port 45. Accordingly, the distal end portion 70 of vane 7 is prevented from being unnecessarily strongly pressed on the inside peripheral surface 80 of cam ring 8, as compared to cases where back pressure chamber br is adapted to receive a high hydraulic pressure from a discharge port. This results in reduction in the loss torque due to friction between the distal end portion 70 of vane 7 and the inside peripheral surface 80 of cam ring 8. In other words, this feature serves to reduce the frictional resistance to the sliding movement of the distal end portion 70 of vane 7 on the inside peripheral surface 80 of cam ring 8, and thereby reduce the power loss, as compared to cases where all of the proximal end portions 71 of vane 7 positioned in the suction region RE1 are applied with a discharge-side pressure.

On the other hand, on the positive y side, the distal end portion 70 of vane 7 is subject to pressure from discharge port 44, whereas the proximal end portion 71 of vane 7 is subject to pressure from discharge-side back pressure port 46. Since discharge-side back pressure port 46 is hydraulically connected to discharge port 44 through second communication passage 492, the distal end portion 70 and proximal end portion 71 of vane 7 are subject to substantially the same pressure. Accordingly, the distal end portion 70 of vane 7 is prevented from being unnecessarily strongly pressed on the inside peripheral surface 80 of cam ring 8. This serves to reduce the loss torque due to friction between the distal end portion 70 of vane 7 and the inside peripheral surface 80 of cam ring 8.

In summary, in pump 1, suction-side back pressure port 45 and discharge-side back pressure port 46 are separately provided for back pressure chambers br, so that both in the suction region RE1 and in the discharge region RE2, the distal end portion 70 and proximal end portion 71 of vane 7 are subject to substantially the same pressure. This feature serves to suitably press the vane 7 on cam ring 8 by the centrifugal force, while suppressing the frictional resistance between vane 7 and cam ring 8. This serves to reduce wear between vane 7 and the inside peripheral surface 80 of cam ring 8, and reduce the power loss, because the required driving torque for rotating the rotor 6 is reduced. In this way, pump 1 is formed as an efficient low-torque type pump where: the required driving torque is smaller with respect to rotational speed; the fuel efficiency is enhanced by reduction in the power loss; and the discharge rate is larger even if the exterior size is identical (i.e. pump 1 can be formed compact), as compared to typical variable displacement pumps.

<Prevention of Flow Through Vane by Vane Pressing> As described above, in the suction region RE1, the projection of vane 7 from slot 61 to the inside peripheral surface 80 of cam ring 8 is implemented mainly by the centrifugal force. Accordingly, when the internal combustion engine is operating in a low speed region, for example, when the engine is at start or at idle, rotor 6 is rotating slowly so that the centrifugal force is small, and the distal end portion 70 of vane 7 may be out of contact with the inside peripheral surface 80 of cam ring 8 because the pressing force for distal end portion 70 is insufficient. This is based on the fact that the amount of projection of vane 7 depends on the force acting on vane 7 outwards in the rotor radial direction. The force depends mainly on the centrifugal force, the viscosity of working fluid, and the friction between vane 7 and slot 61. Among those, the contribution of the centrifugal force is highest. When each pump chamber r is positioned in the first closing region RE3 or second closing region RE4, pump chamber r shifts between the suction region RE1 and the discharge region RE2 along with rotation of rotor 6. If vane 7 moves into the first closing region RE3 or second closing region RE4 under a condition that vane 7 is out of contact with the inside peripheral surface 80 of cam ring 8 due to insufficient projection of vane 7, pump 1 may encounter the following problem.

When the rear-side vane 7 of a first pump chamber r is positioned in the first closing region RE3, the front-side vane 7 of the first pump chamber r is positioned in the discharge region RE2 so that the first pump chamber r is hydraulically connected to discharge port 44, and thereby the internal pressure of the first pump chamber r is high, because the length of the first closing region RE3 in the circumferential direction is equal to one pitch. At the moment, the rear-side vane 7 of a second pump chamber r which is adjacent to the first pump chamber r, and behind the first pump chamber r in the rotor rotation direction RD1 is positioned in the suction region RE1, so that the second pump chamber r is hydraulically connected to suction port 43, and thereby the internal pressure of the second pump chamber r is relatively low. When the internal pressure of the first pump chamber r is thus different significantly from that of the second pump chamber r that is adjacent to the first pump chamber r, and the projection of the vane 7 that divides the first and second pump chambers r from one another is insufficient, then it is possible that working fluid leaks or flows from the higher pressure side pump chamber r to the lower pressure side pump chamber r through a clearance between the distal end portion 70 of vane 7 and the inside peripheral surface 80 of cam ring 8. This phenomenon is referred to as vane through flow. The possibility is relatively high when pump 1 is operating at low temperature. The leaking or vane through flow of working fluid can result in a rapid flow of working fluid, and fluctuations in the pressures in discharge port 44 and suction port 43, and thereby cause noises. If so, the pressure in discharge port 44 falls periodically while moving along with rotation of rotor 6, and thereby causes pulsation of the discharge pressure. This causes a decrease in the amount of discharged working fluid, and a fall in the discharge-side pressure, and thereby causes a fall in the pump efficiency, and a fall in the startability of the system (CVT 100) that uses the pump discharge pressure.

In consideration of the problem described above, pump 1 is configured so that the back pressure chamber br for each vane 7 is applied with high pressure, before the vane 7 enters the first closing region RE3. This ensures that vane 7 is pressed outwards in the rotor radial direction, and brought into contact with the inside peripheral surface 80 of cam ring 8, so that the vane 7 liquid-tightly divides and seals the two adjacent pump chambers r from one another. FIG. 8 is a sectional view of pump 1 taken along the line VIII-VIII in FIG. 6. In FIG. 8, the outside periphery of rotor 6, the inside periphery of cam ring 8, the shape of suction-side arc groove 430, etc. are schematically expressed by straight lines, and the projections 62 of rotor 6 are omitted. As shown in FIG. 8, discharge-side back pressure port 46 (discharge-side back pressure arc groove 460) extends also in the suction region RE1, and the beginning end point c of discharge-side back pressure port 46 is located a distance L0 (one pitch) behind the terminal end point B of suction port 43 (suction-side arc groove 430) in the rotor rotation direction RD1. The distance L0 may be larger than or smaller than one pitch. According to this construction, before vane 7 enters the first closing region RE3, i.e. when vane 7 is positioned behind the terminal end point B of suction port 43 in the rotor rotation direction RD1, the back pressure chamber br for the vane 7 is hydraulically connected to discharge-side back pressure port 46. When the back pressure chamber br for vane 7 that is out of contact with the inside peripheral surface 80 of cam ring 8 enters the discharge-side back pressure port 46 in the terminal end portion 436 of suction port 43, the discharge-side pressure is supplied and applied from discharge-side back pressure port 46 to the proximal end portion 71 of vane 7, so that the vane 7 moves outwards in the rotor radial direction, into pressing contact with cam ring 8. When the vane 7 enters the first closing region RE3 beyond the terminal end point B of suction port 43 along with rotation of rotor 6, vane 7 is already pressed into contact with cam ring 8, thus preventing the fluid communication between suction port 43 and discharge port 44. In this way, the liquid tightness of each pump chamber r is maintained when the pump chamber r is moving from the suction region RE1 toward the discharge region RE2. After the vane 7 enters the first closing region RE3, the back pressure chamber br for the vane 7 is hydraulically connected to discharge-side back pressure port 46, and thereby subject to high pressure, so that the vane 7 is maintained in pressing contact with cam ring 8. In this way, the back pressure chamber br for the vane 7 that defines the pump chamber r positioned in the first closing region RE3 between the suction region RE1 and the discharge region RE2 is applied with high pressure, so that the distal end portion 70 of vane 7 is pressed on the inside peripheral surface 80 of cam ring 8 by the differential pressure between the distal end portion 70 and proximal end portion 71 of vane 7. This serves to maintain the liquid tightness of the pump chamber r that is positioned immediately behind the discharge region RE2 in the rotor rotation direction RD1, and provide sealing between the low pressure suction side and the high pressure discharge side. This feature serves to allow vane 7 to move out of slot 61, and thereby allow pump 1 to perform the suction and discharge function normally, even when the viscosity of working fluid is high, for example, during cold start, so that the pressing force for vane 7 based on the centrifugal force is insufficient. The startability of pump 1 at low temperature is thus enhanced.

<Reduction in Loss torque by Range Setting of Discharge-Side Back Pressure Port> If the angular range where the back pressure chamber br for vane 7 is supplied with high pressure before entering the first closing region RE3 is too wide, the loss torque due to friction is increased, and the effect of reduction in the power loss is reduced, because the angular range where vane 7 slides in pressing contact with the inside peripheral surface 80 of cam ring 8 is also wide. The size of a typical variable displacement pump is generally larger than that of a typical fixed displacement pump having the same capacity, due to additional equipment. Accordingly, in a low speed region (or fixed capacity region) where the pump capacity is unchanged, the efficiency of a typical variable displacement pump is lower than a typical fixed displacement pump, namely, the required driving torque of the variable displacement pump is larger than that of the fixed displacement pump if the rotational speed is the same. Although the efficiency of pump 1 is improved as described above, there is a region where the efficiency is lower than that of the fixed displacement type, and the effect of reduction in the power loss is insufficient. Accordingly, it is desirable to further reduce the power loss in a variable displacement pump. In consideration of this point, pump 1 is configured so that the shape of discharge-side back pressure port 46 (the cross-sectional flow area and the position of the beginning end point c) is adjusted so as to optimize the angular range where the back pressure chamber br for vane 7 is supplied with high pressure before entering the first closing region RE3. This serves to prevent the flow through vane 7 between pump chambers r, and reduce the power loss even in a low speed region where the efficiency is relatively low.

When the rotor rotation direction side surface of a first vane 7 whose projection from slot 61 is relatively small passes through the terminal end point B of suction port 43, the rotor reverse rotation direction side surface of a second vane 7 that is adjacent and ahead of the first vane 7 in the rotor rotation direction RD1 passes through the beginning end point C of discharge port 44. Accordingly, if the distal end portion 70 of the first vane 7 is out of contact with the inside peripheral surface 80 of cam ring 8, it is sufficient to supply an amount of working fluid corresponding to the distance between vane 7 and cam ring 8 to the back pressure chamber br for the first vane 7 through discharge-side back pressure port 46, before the rotor rotation direction side surface of the first vane 7 reaches the terminal end point B of suction port 43. If working fluid is so supplied, it is completed that the vane 7 is pressed into contact with the inside peripheral surface 80 of cam ring 8, before the rotor rotation direction side surface of the first vane 7 reaches the terminal end point B of suction port 43. This serves to ensure the liquid tightness of the pump chamber r that is defined by the first and second vanes 7, before the pump chamber r starts to hydraulically communicate with discharge port 44.

It is desirable to complete the supply of the amount of working fluid corresponding to the clearance between the first vane 7 and cam ring 8, when the rotor rotation direction side surface of the first vane 7 has reached a position as close to the terminal end point B of suction port 43 as possible. This is because it is desirable to reduce the range where the distal end portion 70 of vane 7 is in pressing contact with the inside peripheral surface 80 of cam ring 8 behind the terminal end point B of suction port 43 in the rotor rotation direction RD1, and thereby reduce the loss torque, in consideration of the fact that until the moment the supply of the amount of working fluid required to bring the first vane 7 into contact with cam ring 8 is completed, the first vane 7 is out of contact with cam ring 8. Therefore, in pump 1, the shape of discharge-side back pressure port 46 is set so that supply of the amount of working fluid corresponding to the clearance is completed when the rotor rotation direction side surface of the first vane 7 has reached a position as close to the terminal end point B of suction port 43 as possible.

Specifically, the following equation holds, where “A” represents the cross-sectional flow area of a fluid passage from discharge-side back pressure port 46 to the back pressure chamber br for vane 7, i.e. the cross-sectional flow area of discharge-side back pressure port 46 as viewed in the rotor rotation direction RD1, Q represents an amount per unit time (volumetric flow rate) of working fluid flowing from discharge-side back pressure port 46 into the back pressure chamber br, “C” represents a flow rate coefficient, ρ represent the density of working fluid, and ΔP represents the differential pressure through the fluid passage (the difference in pressure between discharge-side back pressure port 46 and back pressure chamber br≈discharge pressure):

Q=C·A·√(2·ΔP/ρ)

A quantity ∫Q (time integral of Q), which is a total amount of working fluid supplied to back pressure chamber br for vane 7, is proportional to a product of a time period T when back pressure chamber br for vane 7 is hydraulically connected to discharge-side back pressure port 46, and the cross-sectional flow area A. The time period T depends on the rotational speed of rotor 6 (or the travel speed of vane 7), and a travel distance L* of vane 7 in the rotor rotation direction RD1 in discharge-side back pressure port 46 (i.e. the angular range of travel of back pressure chamber br from the beginning end point c of discharge-side back pressure port 46). If the rotational speed of rotor 6 is assumed to be constant, the time period T is determined by the travel distance L*. In summary, the quantity ∫Q is determined by the cross-sectional flow area A of discharge-side back pressure port 46 and the travel distance L* (or the position of the beginning end point c).

In pump 1, the distance (angular range) from the beginning end point c of beginning end portion 462 to the beginning end point e of back pressure port main section 468, L, and the cross-sectional flow area of the beginning end portion 462 of discharge-side back pressure port 46, A, are set so that the fluid quantity ∫Q conforms to the amount of working fluid corresponding to the clearance between vane 7 and cam ring 8. In other words, the distance L and cross-sectional flow area A are set so that while vane 7 moves from the beginning end point c of beginning end portion 462 to the beginning end point e of back pressure port main section 468, the fluid quantity ∫Q which is identical to the total quantity supplied to back pressure chamber br so as to bring the distal end portion 70 of vane 7 into contact with the inside peripheral surface 80 of cam ring 8. In this way, discharge-side back pressure port 46 is arranged so that vane 7 is brought into contact with the inside peripheral surface 80 of cam ring 8 at the beginning end point e close to the terminal end point B, so as to prevent the flow through vane 7 between pump chambers r, and suppress the loss torque due to useless pressing contact.

FIG. 9 shows, in the lower part, combinations of the cross-sectional flow area A of the beginning end portion 462 of discharge-side back pressure port 46 and the distance L with which it is possible to reduce the loss torque while preventing the vane through flow, thus bringing the power loss into an allowable region. This relationship may be determined experimentally or estimated on the basis of design values. Pump 1 is configured so that the point defined by the cross-sectional flow area A and the distance L is positioned in a region indicated by hatching pattern in FIG. 9. The allowable region may be defined so that the total loss torque is comparable to or smaller than the loss torque of a typical fixed displacement pump, when in a predetermined low speed region including a fixed displacement region or when in a mode where such a low speed region is frequently used. The power loss of pump 1 can be thus reduced to a level comparable to or lower than that of a typical fixed displacement pump, even when the CVT to which pump 1 is adapted is operating in a mode where a low speed region where the efficiency is relatively low is frequently used. Also, the power loss of pump 1 can be reduced to a level comparable to or lower than that of a typical fixed displacement pump, even when pump 1 is used as a fluid pressure supply source for a power steering system which constantly uses a low speed region in which the efficiency is relatively low.

The cross-sectional flow area A and the distance L are set in such a desirable region (indicated by hatching pattern in FIG. 9) that even if vane 7 starts to contact the cam ring 8 at a point behind the beginning end point e of back pressure port main section 468 in the rotor rotation direction RD1 under the influence of rotational speed, fluid temperature, and others, the loss torque due to pressing contact of vane 7 (vane loss torque) is below an upper limit of an allowable range. If vane 7 is maintained in contact with cam ring 8 in the suction region RE1, vane 7 continues to be in pressing contact with cam ring 8 after passing through the beginning end point c of the beginning end portion 462, so that the loss torque becomes equal to the upper limit of the desirable region. The maximum allowable value of the distance L is set to a value Lmax that is on the boundary of the allowable range of the vane loss torque, as shown in FIG. 9.

On the other hand, if the vane 7 starts to contact the cam ring 8 at a point ahead of the beginning end point e of back pressure port main section 468 in the rotor rotation direction RD1 under the influence of rotational speed, fluid temperature, and others, the back pressure chamber br is supplied with working fluid at a larger flow rate after vane 7 passes through the beginning end point e than before, because the cross-sectional flow area of back pressure port main section 468 is set larger than that of beginning end portion 462 in discharge-side back pressure port 46. This feature serves to ensure the prevention of vane through flow, because supply of the amount of working fluid corresponding to the clearance between vane 7 and cam ring 8 is completed before the rotor rotation direction side surface of vane 7 passes through the beginning end point e of back pressure port main section 468 and then reaches the terminal end point B of suction port 43. Pump 1 may be modified so that when the rotor rotation direction side surface of vane 7 reaches the terminal end point B of suction port 43, supply of the required amount of working fluid is completed. For example, the beginning end point e of back pressure port main section 468 may be moved to be identical to the terminal end point B of suction port 43 so that the beginning end portion 462 extends from the beginning end point c to the terminal end point B. In such cases, the range where vane 7 is in sliding contact is further reduced to reduce the loss torque more effectively. The desirable position of the beginning end point c (or the desirable range of the distance L) for such cases may be defined with reference to the position of the terminal end point B of suction port 43.

<Noise Reduction by Throttling Portion> Even in the construction that discharge-side back pressure port 46 is formed so as to reduce the loss torque while preventing the vane through flow as described above, noise can be generated if the cross-sectional flow area A is large. When high pressure working fluid starts to flow through the large cross-sectional flow area A of discharge-side back pressure port 46 to back pressure chamber br under condition that vane 7 is out of contact with cam ring 8, it is possible that working fluid rapidly flows into back pressure chamber br so that vane 7 moves toward and collapses hard with cam ring 8, thereby generating noise.

The foregoing problem is solved by pump 1 in which discharge-side back pressure port 46 is provided with beginning end portion 462 that has a reduced cross-sectional flow area A, and thus forms a throttling portion. When the back pressure chamber br (proximal end portion 610 of slot 61) for vane 7 is positioned at beginning end portion 462 (from the beginning end point c to the beginning end point e of back pressure port main section 468), working fluid flows from back pressure port main section 468 through beginning end portion 462 to back pressure chamber br. Since the cross-sectional flow area of beginning end portion 462 is set smaller than that of back pressure port main section 468, the flow rate of working fluid supplied to back pressure chamber br (flow rate Q) is restricted.

Specifically, the cross-sectional flow area A of beginning end portion 462 is adjusted so that the travel speed of vane 7 outwards in the rotor radial direction, V, when distal end portion 70 is contacting the inside peripheral surface 80 of cam ring 8, is optimized, and thereby noise due to contact of vane 7 is within an allowable region. For example, speed V is set so as to permit a some level of noise during cold start, and suppress the occurrence of noise while pump 1 is at idle. The speed V is related to the cross-sectional area S of vane 7 ((pressure receiving area)=(size in the rotor rotation direction RD1)×(size in the z-axis direction)), and the cross-sectional flow area A of beginning end portion 462, as follows:

V=Q/S=C·A/S·√(2·ΔP/ρ), or

H=C/V·√(2·ΔP/ρ), where H represents an area ratio S/A.

Using the above equation, the speed V is optimized by adjusting the area ratio H. In other words, the cross-sectional flow area A of beginning end portion 462 is adjusted with reference to the cross-sectional area S, to achieve the optimized speed V. Specifically, the cross-sectional flow area A of beginning end portion 462 is set within a range from a predetermined minimum value Amin to a predetermined maximum value Amax. The maximum value Amax is determined depending on an allowable noise level. The minimum value Amin is determined depending on the distance L.

FIG. 9 shows, in the upper part, a relationship between the cross-sectional flow area A of discharge-side back pressure port 46, and the noise level. The relationship may be experimentally found or estimated on the basis of design values. Pump 1 is configured so that the cross-sectional flow area A of the beginning end portion 462 of discharge-side back pressure port 46 is set within the desirable range from Amin to Amax, and thereby the noise level is below an upper limit of the allowable range. As a result, allowable combinations of the cross-sectional flow area A and distance L are positioned within the region indicated by hatching pattern in FIG. 9. Accordingly, when the back pressure chamber br of vane 7 that is out of contact with cam ring 8 in the suction region RE1 moves to overlap with the discharge-side back pressure port 46, the throttling function of beginning end portion 462 serves to is restrict the flow rate Q of working fluid flowing into back pressure chamber br. As a result, the speed V when vane 7 moves into contact with cam ring 8 at the beginning end point e is reduced, so that the speed of vane 7 when vane 7 collapses with cam ring 8 is suppressed, and thereby the noise due to contact of vane 7 is suppressed.

According to the throttling effect by beginning end portion 462, the flow rate Q of working fluid discharged from the back pressure port main section 468 is restricted, so that the pressure in back pressure port main section 468 is prevented from fluctuating or pulsating, and thereby the hydraulic force applied to vane 7 from back pressure chamber br that is hydraulically connected to back pressure port main section 468 becomes substantially constant. In this way, in the discharge region RE2, each vane 7 is maintained in stable contact with cam ring 8.

The beginning end portion 462 has a substantially rectangular section as viewed in the z-axis direction, where the depth in the z-axis direction is constant as followed in the rotor rotation direction. Namely, the size of beginning end portion 462 in the rotor radial direction is substantially constant as followed in the rotor rotation direction RD1, and the depth of beginning end portion 462 is also substantially constant. Accordingly, the cross-sectional flow area A of beginning end portion 462 is substantially constant as followed in the rotor rotation direction RD1, so that the flow rate Q of working fluid supplied to back pressure chamber br for vane 7 that is positioned at beginning end portion 462 is substantially constant. This makes it possible to easily set the speed V of vane 7 that moves into contact with cam ring 8.

Comparison in Operation and Effect with Comparative Examples

FIG. 10 is a sectional view of a vane pump according to a first comparative example, which corresponds to the sectional view of FIG. 8. FIG. 11 is a sectional view of a vane pump according to a second comparative example, which corresponds to the sectional view of FIG. 8. As shown in FIG. 10, in the first comparative example, discharge-side back pressure port 46 (discharge-side back pressure arc groove 460) is formed to extend also in the suction region RE1, but discharge-side back pressure port 46 has a beginning end point c1 closer to the terminal end point B of suction port 43, where the distance L1 between the beginning end point c1 and the terminal end point B is equal to a value that is much smaller than the lower limit value Lmin of the desirable range (L1<<Lmin). Moreover, the cross-sectional flow area A of discharge-side back pressure port 46 is the same as that of back pressure port main section 468 according to the first embodiment, and equal to a value A0 that is much larger than the upper limit Amax of the desirable range (A0>>Amax).

In the first comparative example, the amount of working fluid supplied to back pressure chamber br for vane 7 that is entering the first closing region RE3 is to insufficient so that the projection of vane 7 is delayed to allow the vane through flow. Specifically, the combination of the cross-sectional flow area A0 and the distance L1 is positioned out of the desirable region in FIG. 9, so that the occurrence of vane through flow vane is possible. Accordingly, in the first comparative example, the fluid quantity ∫Q of working fluid supplied to back pressure chamber br during the period when the rotor rotation direction side surface of vane 7 moves from the beginning end point c1 to the terminal end point B is below the amount corresponding to the clearance between vane 7 and cam ring 8 (the amount for eliminating the clearance). As a result, the vane through flow occurs, because the distal end portion 70 of vane 7 is out of contact with the inside peripheral surface 80 of cam ring 8 when the rotor rotation direction side surface of vane 7 has reached the terminal end point B.

Moreover, in the first comparative example, the travel speed of vane 7 when vane 7 collapses with cam ring 8 is high, because the cross-sectional flow area A is excessive. Specifically, the cross-sectional flow area A0 of the first comparative example is larger than the upper limit Amax of the region where noise level is in the allowable range. Since the discharge-side back pressure port 46 of the first comparative example is provided with no such throttling portion (beginning end portion 462 according to the first embodiment), working fluid flows rapidly into back pressure chamber br. Accordingly, when vane 7 contacts the inside peripheral surface 80 of cam ring 8 after passing through the terminal end point B, the speed V of vane 7 is high. As a result, the noise due to contact or collapse of vane 7 is out of the allowable range.

As shown in FIG. 11, discharge-side back pressure port 46 according to the second comparative example has a beginning end point c2 that is substantially identical to the beginning end point c according to the first embodiment, where the distance L2 between the beginning end point c2 of discharge-side back pressure port 46 and the terminal end point B of suction port 43 is substantially equal to the distance L0 according to the first embodiment, and smaller than upper limit value Lmax of the desirable range (L2≈L0<Lmax). Moreover, the cross-sectional flow area A of discharge-side back pressure port 46 in the suction region RE1 is the same as that of back pressure port main section 468 according to the first embodiment, and equal to a value A0 that is much larger than the upper limit Amax of the desirable range (A0>>Amax).

In the second comparative example, the amount of working fluid supplied to back pressure chamber br for vane 7 that is entering the first closing region RE3 is sufficient to prevent the vane through flow. However, vane 7 moves into sliding contact with cam ring 8 in earlier timing than in the first embodiment. This is because the cross-sectional flow area A of discharge-side back pressure port 46 of the second comparative example is larger than that of the first embodiment, so that the fluid quantity ∫Q of working fluid supplied to back pressure chamber br exceeds the amount corresponding to the clearance between vane 7 and cam ring 8 (the amount for eliminating the clearance), when the rotor rotation direction side surface of vane 7 has traveled from the beginning end point c2 to a point F which is behind the point for the first embodiment that is a distance L** ahead of the beginning end point c2. As a result, the region where the distal end portion 70 of vane 7 is unnecessarily pressed on the inside peripheral surface 80 of cam ring 8 before passing through the terminal end point B, is larger than in the first embodiment, so that the loss torque is larger, but within the desirable range indicated by hatching pattern in FIG. 9.

On the other hand, in the second comparative example, the speed of vane 7 when vane 7 collapses with cam ring 8 is high, because the discharge-side back pressure port 46 of the first comparative example is provided with no such throttling portion (beginning end portion 462 according to the first embodiment) so that the cross-sectional flow area A is excessive. Specifically, the cross-sectional flow area A0 of the first comparative example is larger than the upper limit Amax of the region where noise level is in the allowable range. Accordingly, as in the first comparative example, when vane 7 contacts the inside peripheral surface 80 of cam ring 8 after passing through the terminal end point B, the speed V of vane 7 is high. As a result, the noise due to collapse of vane 7 is out of the allowable range.

In contrast, in the first embodiment, the cross-sectional flow area A of the beginning end portion 462 of discharge-side back pressure port 46 in the suction region RE1 and the distance L are set in the region indicated by hatching pattern in FIG. 9, so as to simultaneously optimize the sealing effect, the loss torque, and the noise level, in consideration of the relationship shown in FIG. 9 between those parameters. Accordingly, it is possible to prevent the vane through flow, suppress the pulsation and noise, and suppress adverse effects on the pump efficiency and startability. Moreover, it is possible to reduce the region where vane 7 is unnecessarily pressed on cam ring 8, and thereby reduce the power loss. Still moreover, it is possible to prevent working fluid from rapidly flowing into back pressure chamber br for vane 7, and thereby further suppress the occurrence of noise. These advantageous effects are more significant, especially when in a low temperature condition where the viscosity of working fluid is relatively high, or when in a drive mode where the low speed region of the internal combustion engine is frequently used.

Advantageous Effects by First Embodiment

The following summarizes the advantageous effects produced by the pump 1 according to the first embodiment.

<1> A vane pump (1) comprises: a rotor (6) adapted to be rotated by a drive shaft (5), the rotor (6) including a plurality of slots (61) at an outside periphery (60) of the rotor (6); a plurality of vanes (7) mounted in corresponding ones of the slots (61), and adapted to project from, and travel inwards and outwards of the corresponding slots (61); a cam ring (8) adapted to be eccentric with respect to the rotor (6), the cam ring (8) surrounding the rotor (6); and a plate (first or second plate 41 or 42) arranged to face an axial end of the rotor (6), and define a plurality of pump chambers (r) in cooperation with the rotor (6), the vanes (7), and the cam ring (8), wherein the plate (first plate 41) includes at a side facing the rotor (6): a suction port (43) opened in a suction region in which each pump chamber (r) gradually expands while moving along with rotation of the rotor (6); a discharge port (44) opened in a discharge region in which each pump chamber (r) gradually contracts while moving along with rotation of the rotor (6); a first back pressure port (suction-side back pressure port 45) arranged to receive a suction-side fluid pressure, and hydraulically communicate with a proximal end portion (610, or back pressure chamber br) of at least a first one of the slots (61) corresponding to a first one of the vanes (7) positioned in the suction region; and a second back pressure port (46) arranged to hydraulically communicate with a proximal end portion (610, or back pressure chamber br) of at least a second one of the slots (61) corresponding to a second one of the vanes (7) whose distal end portion (70) is positioned at a terminal end portion (close to terminal end point B) of the suction port (43), wherein the second back pressure port (46) includes: a first portion (back pressure port main section 468) arranged to receive a discharge-side fluid pressure; and a throttling portion (beginning end portion 462) arranged to restrict a flow of fluid between the first portion (back pressure port main section 468) and the proximal end portion (610, or back pressure chamber br) of the second slot (61). This construction is effective for reducing the power loss, enhancing the operation of the pump at low temperature, and reducing the noise level.

<2> In the vane pump according to item <1>, the throttling portion (beginning end portion 462) has a cross-sectional flow area (A) that is substantially constant as followed in a direction of rotation of the rotor (6). This feature makes it possible to easily set the speed V of vane 7 when vane 7 moves into contact with cam ring 8, by adjusting the depth of the throttling portion (beginning end portion 462).

<3> In the vane pump according to item <1> or <2>: the second vane (7) is behind in a direction of rotation of the rotor (6) and adjacent to a third one of the vanes (7) whose distal end portion (70) is positioned between a terminal end (terminal end point B) of the suction port (43) and a beginning end (beginning end point C) of the discharge port (44); and the second back pressure port (discharge-side back pressure port 46) is arranged to supply the proximal end portion (610, or back pressure chamber br) of the second slot (61) at least with an amount of working fluid, during a period before the second vane (7) passes through the terminal end (B) of the suction port (43) after the proximal end portion (610, br) of the second slot (61) starts to hydraulically communicate with the second back pressure port (46), wherein the amount of working fluid is sufficient to bring the distal end portion (70) of the second vane (7) into contact with an inside peripheral surface (80) of the cam ring (8). This feature is effective for enhancing the operation of the pump at low temperature by effectively preventing the vane through flow.

Second Embodiment

In the first embodiment, the throttling portion (beginning end portion 462) has a rectangular cross-section with a substantially constant depth and a substantially constant width as viewed and followed in the rotor rotation direction RD1, so that the cross-sectional flow area A is substantially constant as followed in the rotor rotation direction RD1. Alternatively, the shape of the throttling portion (beginning end portion 462) may be modified so that the cross-sectional flow area A changes as followed in the rotor rotation direction RD1, in consideration of the viscosity of working fluid, the density of working fluid, and other factors, as shown in FIGS. 12A to 15. In the examples shown in FIGS. 12A to 15, the edge 467 of back pressure port main section 468 is rectangular, not semicircular as in the first embodiment. The other parts are the same as in the first embodiment, and accordingly, description of the other parts is omitted.

In the examples shown in FIGS. 12A to 15, the fluid quantity ∫Q is set by combination of the cross-sectional flow area A and distance L of the throttling portion (beginning end portion 462), so as to prevent the vane through flow, and the unnecessary pressing of vane 7, as in the first embodiment. Since the cross-sectional flow area of beginning end portion 462 is not constant as followed in the rotor rotation direction RD1 as in the first embodiment, the average of the cross-sectional flow area of beginning end portion 462, which is averaged in the rotor rotation direction RD1, may be used as the cross-sectional flow area A to set the fluid quantity ∫Q.

In the second embodiment, beginning end portion 462 is formed so that the cross-sectional flow area of beginning end portion 462 increases as followed in the rotor rotation direction RD1. This feature makes it possible to set the ejecting speed of vane 7 that is passing through the beginning end portion 462 as follows. FIGS. 12A to 12D are plan views of beginning end portions 462 according to variations of the second embodiment in the z-axis direction. In the examples shown in FIGS. 12A to 12B, the width of beginning end portion 462 in the rotor radial direction is set to increase as followed in the rotor rotation direction RD1, whereas the bottom (negative z side surface) of beginning end portion 462 is substantially flat, and the depth of beginning end portion 462 is substantially constant, as in the first embodiment. However, in consideration of the fact that the width (average width) of beginning end portion 462 is smaller than that in the first embodiment, the depth of beginning end portion 462 is set larger than that in the first embodiment, so that the cross-sectional flow area is not reduced. The shape of the bottom may be modified arbitrarily.

In the example of FIG. 12A, the shape of beginning end portion 462 as viewed in the z-axis direction is substantially in the form of an acute angle triangle whose width gradually increases as followed in the rotor rotation direction RD1 at a predetermined substantially constant rate to a predetermined value that is smaller than the width of back pressure port main section 468. Accordingly, while vane 7 passes through beginning end portion 462, the cross-sectional flow area of a passage to back pressure chamber br gradually increases from zero to a predetermined value at a substantially constant rate. As a result, the flow rate Q of working fluid supplied to back pressure chamber br gradually increases from zero, so that the ejecting speed of vane 7 is low at first, and gradually increases at a substantially constant rate. The shape of FIG. 12A is desirable, when such characteristics are desired.

In the example of FIG. 12B, the shape of beginning end portion 462 as viewed in the z-axis direction is substantially in the form of a trapezoid whose width gradually increases as followed in the rotor rotation direction RD1 at a predetermined substantially constant rate from a predetermined smaller value to a predetermined larger value that is smaller than the width of back pressure port main section 468. Accordingly, while vane 7 passes through beginning end portion 462, the cross-sectional flow area of a passage to back pressure chamber br gradually increases from a predetermined smaller value to a predetermined larger value at a substantially constant rate. As a result, the flow rate Q of working fluid supplied to back pressure chamber br is above zero, at first, and then gradually increases, so that the ejecting speed of vane 7 is moderate at first, and then gradually increases at a substantially constant rate. This feature serves to shorten the period in which vane 7 moves into contact with the inside peripheral surface 80 of cam ring 8, as compared to the shape of FIG. 12A. The shape of FIG. 12B is desirable, when such characteristics are desired.

In the example of FIG. 12C, the shape of beginning end portion 462 as viewed in the z-axis direction is substantially in the form of a semi-ellipse whose width gradually increases as followed in the rotor rotation direction RD1 from zero to a predetermined value that is smaller than the width of back pressure port main section 468. The rate of increase is large at first, and then decreases. Accordingly, while vane 7 passes through beginning end portion 462, the cross-sectional flow area of a passage to back pressure chamber br gradually increases from zero to a predetermined value at the rate that is large at first, and then decreases. As a result, the flow rate Q of working fluid supplied to back pressure chamber br rapidly increases from zero, and then slowly increases, so that the ejecting speed of vane 7 rapidly increases at first, and then slowly increases. This feature serves to shorten the period in which vane 7 moves into contact with the inside peripheral surface 80 of cam ring 8, similar to the shape of FIG. 12B. The shape of FIG. 12C is desirable, when such characteristics are desired.

In the example of FIG. 12D, the shape of beginning end portion 462 as viewed in the z-axis direction is a combination of the rectangular shape according to the first embodiment and the trapezoidal shape of FIG. 12B, whose width is constant at first, and then gradually increases as followed in the rotor rotation direction RD1 at a predetermined substantially constant rate to a predetermined value that is smaller than the width of back pressure port main section 468. Accordingly, while vane 7 passes through beginning end portion 462, the cross-sectional flow area of a passage to back pressure chamber br is constant at first, and then gradually increases at a substantially constant rate. As a result, the flow rate Q of working fluid supplied to back pressure chamber br is constant, at first, and then gradually increases, so that the ejecting speed of vane 7 is constant at first, and then gradually increases at a substantially constant rate. The ejecting speed of vane 7 does not change significantly as in the examples shown in FIGS. 12A to 12C. As compared to the example where the beginning end portion 462 is rectangular, the pressing of vane 7 to cam ring 8 is ensured. The shape of FIG. 12D is desirable, when such characteristics are desired.

FIGS. 13A and 13B are side sectional views of the beginning end portions 462 according to other variations of the second embodiment. In these variations, the bottom of beginning end portion 462 is inclined as followed in the rotor rotation direction RD1 so that the depth of beginning end portion 462 in the z-axis direction gradually increases as followed in the rotor rotation direction RD1. The width of beginning end portion 462 in the rotor radial direction is substantially constant as followed in the rotor rotation direction RD1.

In the example of FIG. 13A, the bottom of beginning end portion 462 is composed of inclined surfaces and a level surface, specifically, composed of a first inclined surface where the depth of beginning end portion 462 gradually increases at a substantially constant rate from zero to a predetermined value as followed in the rotor rotation direction RD1, an intermediate level surface where the depth of beginning end portion 462 is constant as viewed in the rotor rotation direction RD1, and a second inclined surface where the depth of beginning end portion 462 gradually increases at a substantially constant rate from the first value to a second predetermined value, wherein the second inclined surface is connected to the back pressure port main section 468. The inclination of the first inclined surface is larger than that of the second inclined surface. Accordingly, while vane 7 passes through beginning end portion 462, the cross-sectional flow area of a passage to back pressure chamber br gradually increases from zero to a predetermined value at a constant rate, and then becomes constant, and then gradually increases at a substantially constant and slower rate. As a result, the flow rate Q of working fluid supplied to back pressure chamber br changes similarly, so that the ejecting speed of vane 7 relatively rapidly increases, and then becomes constant, and then relatively slowly increases. This is effective for reducing the acceleration of vane 7 temporarily, while ensuring that vane 7 is pressed on the inside peripheral surface 80 of cam ring 8. The shape of FIG. 13A is desirable, when such characteristics are desired. The shape of beginning end portion 462 may be modified so that the inclination of the first inclined surface is smaller than that of the second inclined surface.

In the example of FIG. 13B, the bottom of beginning end portion 462 is composed of an inclined surface, so that the depth of beginning end portion 462 gradually increases at a substantially constant rate from zero to a predetermined value that is smaller than the depth of back pressure port main section 468. Accordingly, while vane 7 passes through beginning end portion 462, the cross-sectional flow area of a passage to back pressure chamber br gradually increases from zero to a predetermined value at a constant rate. As a result, the flow rate Q of working fluid supplied to back pressure chamber br changes similarly, so that the ejecting speed of vane 7 is low at first, and gradually accelerated to increase at a substantially constant rate. The shape of FIG. 13B is desirable, when such characteristics are desired. The shapes of FIGS. 12A to 12E and the shapes of FIGS. 13A and 13B may be combined so as to achieve a desirable set of characteristics.

In the second embodiment, the feature that beginning end portion 462 is formed so that the cross-sectional flow area of beginning end portion 462 gradually increases as followed in the rotor rotation direction RD1, is effective for reliably pressing the vane 7 on the inside peripheral surface 80 of cam ring 8. In other words, the beginning end portion 462 according to the second embodiment serves as a part (from the beginning end point e to the terminal end point B) of back pressure port main section 468 according to the first embodiment, i.e. serves to supply a large amount of working fluid to reliably prevent the vane through flow, because beginning end portion 462 according to the second embodiment has a larger cross-sectional flow area than the beginning end portion 462 according to the first embodiment. Accordingly, in the second embodiment, the angular position of the beginning end point e of back pressure port main section 468 may be modified to be identical to the angular position of the terminal end point B of suction port 43, and the distance from the beginning end point c of beginning end portion 462 to the beginning end point e of back pressure port main section 468 may be set equal to about one pitch (L0).

Advantageous Effect by Second Embodiment

In the second embodiment, the throttling portion (beginning end portion 462) has a cross-sectional flow area (A) that increases as followed in a direction of rotation of the rotor (6). This produces an advantageous effect of further preventing the vane through flow, in addition to the effects according to the first embodiment.

Third Embodiment

In the third embodiment, beginning end portion 462 is formed so that the cross-sectional flow area of beginning end portion 462 gradually decreases as followed in the rotor rotation direction RD1. This feature makes it possible to set the ejecting speed of vane 7 when vane 7 is passing through the beginning end portion 462. FIGS. 14A to 14D are plan views of beginning end portions 462 according to variations of the third embodiment. In these examples, the width of beginning end portion 462 in the rotor radial direction is set to decrease in the rotor rotation direction RD1. The bottom shape and depth of beginning end portion 462 are the same as in the second embodiment shown in FIGS. 12A to 12E.

In the example of FIG. 14A, the shape of beginning end portion 462 as viewed in the z-axis direction is a combination of a substantially circular end portion and a substantially rectangular portion, where the width of beginning end portion 462 in the rotor radial direction (cross-sectional flow area of passage to back pressure chamber br) rapidly increases and decreases in the circular end portion, and then becomes constant in the rectangular portion, as followed in the rotor rotation direction RD1. Accordingly, while vane 7 passes through beginning end portion 462, the flow rate Q of working fluid supplied to back pressure chamber br changes similarly as the width of beginning end portion 462, so that the ejecting speed of vane 7 increases and decreases rapidly at first, and then becomes substantially constant. The shape of FIG. 14A is desirable, when such characteristics are desired.

In the example of FIG. 14B, the shape of beginning end portion 462 as viewed in the z-axis direction is substantially in the form of a triangle that is directed opposite to the triangle of FIG. 12A, where the width of beginning end portion 462 in the rotor radial direction (cross-sectional flow area of passage to back pressure chamber br) gradually decreases from a predetermined value, which is smaller than that of back pressure port main section 468, to zero at a substantially constant rate as followed in the rotor rotation direction RD1. Accordingly, while vane 7 passes through beginning end portion 462, the flow rate Q of working fluid supplied to back pressure chamber br changes similarly as the width of beginning end portion 462, so that the ejecting speed of vane 7 is relatively fast at first, and then decreases at a substantially constant rate to a value close to zero. The shape of FIG. 14B is desirable, when such characteristics are desired.

In the example of FIG. 14C, the shape of beginning end portion 462 as viewed in the z-axis direction is substantially in the form of a semi-ellipse that is directed opposite to the shape of FIG. 12C, where the width of beginning end portion 462 in the rotor radial direction (cross-sectional flow area of passage to back pressure chamber br) gradually decreases from a predetermined value, which is smaller than that of back pressure port main section 468, to zero as followed in the rotor rotation is direction RD1. The rate of decrease is relatively small at first, and is relatively large at last. Accordingly, while vane 7 passes through beginning end portion 462, the flow rate Q of working fluid supplied to back pressure chamber br changes similarly as the width of beginning end portion 462, so that the ejecting speed of vane 7 is relatively fast at first, and decreases slowly at first, and then decreases rapidly. The shape of FIG. 14C is desirable, when such characteristics are desired.

In the example of FIG. 14D, the shape of beginning end portion 462 as viewed in the z-axis direction is substantially in the form of a combination of a trapezoid and a rectangular that is directed opposite to the shape of FIG. 12D, where the width of beginning end portion 462 in the rotor radial direction (cross-sectional flow area of passage to back pressure chamber br) gradually decreases from a predetermined value, which is smaller than that of back pressure port main section 468, to zero at a substantially constant rate, and then becomes substantially constant, as followed in the rotor rotation direction RD1. Accordingly, while vane 7 passes through beginning end portion 462, the flow rate Q of working fluid supplied to back pressure chamber br changes similarly as the width of beginning end portion 462, so that the ejecting speed of vane 7 is relatively fast at first, and then decreases at a substantially constant rate, and then becomes constant. The shape of FIG. 14D is desirable, when such characteristics are desired.

FIG. 15 shows another variation of the third embodiment, where the bottom of beginning end portion 462 is inclined so that the depth of beginning end portion 462 in the z-axis direction gradually decreases as followed in the rotor rotation direction RD1. The width of beginning end portion 462 in the rotor radial direction is substantially constant as followed in the rotor rotation direction RD1. Specifically, the depth of beginning end portion 462 gradually decreases at a substantially constant rate from a predetermined value (somewhat smaller than the depth of back pressure port main section 468) to a value close to zero, as followed in the rotor rotation direction RD1. Accordingly, while vane 7 passes through beginning end portion 462, the cross-sectional flow area of passage to back pressure chamber br gradually decreases from a predetermined value to a value close to zero, so that the flow rate Q of working fluid supplied to back pressure chamber br changes similarly, and so that the ejecting speed of vane 7 is relatively fast at first, and then decreases at a substantially constant rate to a value close to zero. The shape of FIG. 15 is desirable, when such characteristics are desired. The shape of beginning end portion 462 may be modified similarly as in the second embodiment shown in FIG. 13A, so that the inclined surface is formed with an intermediate level surface, so as to reduce the deceleration of vane 7 temporarily. The shapes of FIGS. 14A to 14E and the shape of FIG. 15 may be combined to achieve a desirable set of characteristics.

In the third embodiment, at the early stage of the ejecting movement of vane 7, most of the amount of working fluid required for vane 7 to contact the cam ring 8 (for vane 7 to travel the initial clearance between vane 7 and cam ring 8) is supplied to back pressure chamber br. This makes it possible to shorten the length of beginning end portion 462 in the rotor rotation direction RD1 (distance L). On the other hand, the feature that the ejecting speed of vane 7 is reduced at the final stage of the ejecting movement of vane 7 where vane 7 moves into contact with cam ring 8, serves to effectively reduce the noise due to contact of vane 7. Beginning end portion 462 according to the third embodiment is formed so that the cross-sectional flow area of beginning end portion 462 gradually decreases as followed in the rotor rotation direction RD1, and thereby fluid communication between the beginning end portion 462 and back pressure port main section 468 is restricted, as compared to the first and second embodiments. Accordingly, even if supply of working fluid from beginning end portion 462 to back pressure chamber br for vane 7 is started so that the pressure in beginning end portion 462 rapidly falls, the pressure in back pressure port main section 468 is prevented form rapidly changing (decreasing), because the flow rate of working fluid leaking from back pressure port main section 468 to beginning end portion 462 for replenishing the amount supplied to back pressure chamber br is restricted. As a result, as in the first embodiment, beginning end portion 462 according to the third embodiment also serves to prevent the pressure in back pressure port main section 468 from fluctuating or pulsating, and thereby stabilize the pressure applied to vane 7 from back pressure chamber br that is hydraulically connected to back pressure port main section 468.

Advantageous Effect by Third Embodiment

In the third embodiment, the throttling portion (beginning end portion 462) has a cross-sectional flow area (A) that decreases as followed in a direction of rotation of the rotor (6). This feature produces an advantageous effect of enhancing the noise reduction effect, in addition to the effects according to the first embodiment.

The first to third embodiments may be modified as follows. Pump 1 may use fluid other than oils (ATF) as working fluid. Although the vane 7 (or slot 61) is formed to extend in the rotor radial direction, the vane 7 (or slot 61) may be formed to extend with inclination with respect to the rotor radial direction.

The portion of discharge-side back pressure port 46 in suction region RE1 (the portion including the beginning end portion 462) is provided separately from the portion of discharge-side back pressure port 46 in the discharge region RE2. In other words, discharge-side back pressure port 46 may be implemented by: a first port arranged to receive a discharge-side fluid pressure, and hydraulically communicate with a proximal end portion (610, back pressure chamber br) of at least a first one of slots (61) corresponding to a first one of vanes (7) positioned in a discharge region (RE2); and a second port arranged to receive a discharge-side fluid pressure, and hydraulically communicate with a proximal end portion (610, back pressure chamber br) of at least a second one of slots (61) corresponding to a second one of vanes (7) whose distal end portion (70) is positioned at a terminal end portion (B) of a suction port (43).

The entire contents of Japanese Patent Application 2010-000528 filed Jan. 5, 2010 and Japanese Patent Application 2010-062861 filed Mar. 18, 2010 are incorporated herein by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A vane pump comprising: a rotor adapted to be rotated by a drive shaft, the rotor including a plurality of slots at an outside periphery of the rotor; a plurality of vanes mounted in corresponding ones of the slots, and adapted to project from, and travel inwards and outwards of the corresponding slots; a cam ring adapted to be eccentric with respect to the rotor, the cam ring surrounding the rotor; and a plate arranged to face an axial end of the rotor, and define a plurality of pump chambers in cooperation with the rotor, the vanes, and the cam ring, wherein the plate includes at a side facing the rotor: a suction port opened in a suction region in which each pump chamber gradually expands while moving along with rotation of the rotor; a discharge port opened in a discharge region in which each pump chamber gradually contracts while moving along with rotation of the rotor; a first back pressure port arranged to receive a suction-side fluid pressure, and hydraulically communicate with a proximal end portion of at least a first one of the slots corresponding to a first one of the vanes positioned in the suction region; and a second back pressure port arranged to hydraulically communicate with a proximal end portion of at least a second one of the slots corresponding to a second one of the vanes whose distal end portion is positioned at a terminal end portion of the suction port, wherein the second back pressure port includes: a first portion arranged to receive a discharge-side fluid pressure; and a throttling portion arranged to restrict a flow of fluid between the first portion and the proximal end portion of the second slot.
 2. The vane pump as claimed in claim 1, wherein the throttling portion has a cross-sectional flow area that is substantially constant as followed in a direction of rotation of the rotor.
 3. The vane pump as claimed in claim 1, wherein the throttling portion has a cross-sectional flow area that increases as followed in a direction of rotation of the rotor.
 4. The vane pump as claimed in claim 1, wherein the throttling portion has a cross-sectional flow area that decreases as followed in a direction of rotation of the rotor.
 5. The vane pump as claimed in claim 1, wherein: the second vane is behind in a direction of rotation of the rotor and adjacent to a third one of the vanes whose distal end portion is positioned between a terminal end of the suction port and a beginning end of the discharge port; and the second back pressure port is arranged to supply the proximal end portion of the second slot at least with an amount of working fluid, during a period before the second vane passes through the terminal end of the suction port after the proximal end portion of the second slot starts to hydraulically communicate with the second back pressure port, wherein the amount of working fluid is sufficient to bring the distal end portion of the second vane into contact with an inside peripheral surface of the cam ring.
 6. The vane pump as claimed in claim 1, wherein: each of the vanes extends in a radial direction of the rotor; and the second back pressure port overlaps with the suction port in a circumferential direction of the plate.
 7. The vane pump as claimed in claim 1, wherein the throttling portion has a cross-sectional flow area that changes as followed in a direction of rotation of the rotor.
 8. The vane pump as claimed in claim 7, wherein the cross-sectional flow area of the throttling portion changes with a change in depth of the throttling portion.
 9. The vane pump as claimed in claim 1, wherein the throttling portion has a smaller depth than the first portion. 